Patent Publication Number: US-2016224707-A1

Title: Apparatus and method for magnetic field simulation

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2015-018105, filed on Feb. 2, 2015, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein relate to an apparatus and method for magnetic field simulation. 
     BACKGROUND 
     As computers have become more and more powerful, the numerical analysis has been increasingly used to simulate various physical phenomena. The finite element method (FEM) is known as a technique for numerical analysis and used to numerically find approximate solutions for differential equations that are hard to solve with an analytical method. Briefly, the method subdivides a two-dimensional or three-dimensional problem space into small regions called “elements” and calculates an approximate solution for the original equations by applying, for each element, relatively simple interpolation functions (e.g., linear functions) to approximate the original equations. For example, a computer obtains an approximate solution by solving a large-scale system of linear equations with a sparse coefficient matrix. 
     There are two types of FEM, called “node-based” and “edge-based,” that use different places for variables representing unknowns to be solved. The node-based FEM assigns a variable to each node (vertex) of elements, whereas the edge-based FEM assigns it to each edge of elements. For the purpose of magnetic field analysis, the edge-based FEM is advantageous over the node-based FEM in term of accuracy of numerical analysis, since it preserves magnetic flux and a line integral along a loop is zero. Edge-based numerical techniques are thus used for a magnetic field simulation. 
     As an example of edge-based FEM, a method for solving partial differential equations is proposed to analyze variations of a physical quantity in the modeling space in which some of multiple objects are moving (e.g., a coil moving relative to an iron core). This method divides an individual object and its surrounding area into a plurality of elements. Different objects (e.g., iron core and coil) are allowed to have different element shapes. In addition, elements of one object are allowed to overlap with elements of other objects in the space. These things facilitate entry of model data. 
     The above method determines new positions of moving objects in the model, thereby detecting elements that overlap with others. Two overlapping elements, however, do not necessarily share their edges. Accordingly, the method interconnects data of these overlapping elements by using interpolation to insert internal vectors of one element into a boundary edge of the other element. In this “interpolation,” inner products are calculated between each internal vector of one element and a direction vector representing the boundary edge of the other element, thus obtaining a component term along the boundary edge. Since the above process has interconnected overlapping elements, the proposed method now produces a coefficient matrix of simultaneous equations for the entire set of elements and solves these simultaneous equations. 
     In the related techniques, a simulator apparatus that performs an electromagnetic field analysis with a finite-difference time-domain (FDTD) method is proposed. Also proposed is an analyzer apparatus for solving simultaneously an electromagnetic field problem, temperature field problem, and fluid field problem by using several kinds of methods including edge-based FEM. 
     See, for example, the following patent documents: 
     Japanese Laid-open Patent Publication No. 9-44473 
     Japanese Laid-open Patent Publication No. 2004-4054 
     Japanese Laid-open Patent Publication No. 2012-74016 
     One of the applications of edge-based FEM is a magnetic field analysis of an object formed from multiple components whose relative positions vary with time as in a rotating electric motor. It is preferable in this application that the analyzer can use the original set of elements even if their relative positions are changed. However, a change in the component positions could disrupt continuity of some elements on the opposite sides of the boundary between those components. That is, some adjacent elements could loose their shared edges. If independent variables are defined for unknowns at individual edges, and if shared edges of adjacent elements are lost, the flow of magnetic flux among these elements would not be expressed properly in the model. 
     One possible solution for the above problem about elements on opposite sides of the boundary plane is to describe unknowns at the edges of elements on one side, not as independent variables, but as functions of variables of elements on the other side, as in the foregoing method for solving partial differential equations. However, the foregoing method is able to describe an unknown at an edge of a certain element only under the condition that the edge in question is wholly in contact with one or more planes of other elements. When a variation of element positions has caused one part of some element to lose its contact with any other element, the foregoing method is unable to express a flow of magnetic flux at that part. 
     SUMMARY 
     In one aspect, there is provided a non-transitory computer-readable storage medium storing a program. The program causes a computer to perform a procedure including: calculating, based on position data indicating a position of a first plane in a model and first magnetic field data for the first plane, second magnetic field data for an overlapping area of a second plane in the model, the first and second planes respectively belonging to first and second elements of the model, the overlapping area being a part of the second plane that overlaps with the first plane, the second plane having a non-overlapping area that is outside the first plane; and calculating third magnetic field data for the non-overlapping area of the second plane, based on the second magnetic field data and a relative position of the non-overlapping area with respect to the overlapping area. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates a magnetic field simulator apparatus according to a first embodiment; 
         FIG. 2  is a block diagram illustrating an exemplary hardware configuration of a magnetic field simulator apparatus; 
         FIGS. 3A and 3B  illustrate examples of unknowns in an edge-based FEM; 
         FIG. 4  illustrates an exemplary model of an electric motor; 
         FIG. 5  illustrates an exemplary model of an electric motor that has rotated; 
         FIG. 6  illustrates an example of master-side and slave-side elements; 
         FIG. 7A to 7D  illustrate various combinations of master-plane and slave-plane shapes; 
         FIG. 8  illustrates a first exemplary overlap of a slave plane with master planes; 
         FIG. 9  illustrates a second exemplary overlap of a slave plane with master planes; 
         FIG. 10  illustrates a third exemplary overlap of a slave plane with master planes; 
         FIG. 11  is a block diagram illustrating an example of functions implemented in the proposed magnetic field simulator apparatus; 
         FIG. 12  illustrates an exemplary structure of geometrical data; 
         FIG. 13  illustrates an exemplary structure of weight data; and 
         FIG. 14  is a flowchart illustrating an exemplary procedure for combining variables. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Several embodiments will be described below with reference to the accompanying drawings. 
     (a) First Embodiment 
       FIG. 1  illustrates a magnetic field simulator apparatus according to a first embodiment. The illustrated magnetic field simulator apparatus  10  analyzes a magnetic field by using a finite element method based on edge elements (edge-based FEM). For example, the magnetic field simulator apparatus  10  simulates a distribution of vector potentials in an object under analysis. The use of an edge-based FEM enables more accurate approximation of physical values that are hard to obtain with an analytical method. 
     The magnetic field simulator apparatus  10  uses a model  13  representing the object under analysis. Preferably this model  13  is three-dimensional. The magnetic field simulator apparatus  10  divides the model  13  into small segments called “elements.” In the case of a three-dimensional model, each element is a tetrahedron having four triangular surfaces or a hexahedron having six quadrangular surfaces. The edge-based FEM calculates variables that have been defined at the edges of each such element to represent unknowns to be solved. The magnetic field simulator apparatus  10  approximates the original equation by using relatively simple interpolation functions (e.g., linear functions) applicable for individual elements. The magnetic field simulator apparatus  10  calculates unknowns in the model  13 , thereby obtaining a field of vector potential or other physical quantity related to the magnetic field. For this calculation, the magnetic field simulator apparatus  10  produces a sparse coefficient matrix representing large-scale linear equations. 
     The first embodiment assumes that the object under analysis is formed from multiple components whose relative positions may vary. For example, the model  13  may represent an electric motor having a stator and a rotor. The stator is the stationary part of the motor, whereas the rotor turns and thus varies its angular position relative to the stator. The magnetic field simulator apparatus  10  simulates variations of a specific physical quantity (e.g., magnetic field) with time. This means that the simulation has to take into account a motion of the model  13  that happens between different time points. It would be preferable if the same model  13  could be used for simulation at different time points without the need for re-dividing it into elements. However, a change in the relative positions of model components disrupts continuity of some adjacent elements at the boundary of those changed components. That is, some of the formerly adjacent elements could lose their shared edges. The edge-based FEM, on the other hand, basically has to define independent variables at individual edges. If a shared edge of adjacent elements is lost, the magnetic flux flow between these elements would not be expressed properly in the model  13 , thus spoiling the accuracy of analysis. 
     The proposed magnetic field simulator apparatus  10  is therefore designed to associate unknowns between adjacent elements that have lost continuity as a result of a change in their relative positions. Specifically, the model  13  includes a first element having a first plane  13   a  and a second element having a second plane  13   b . The two planes  13   a  and  13   b  are located at a boundary of two components whose relative positions have changed. The first plane  13   a  does not share any edge with the second plane  13   b , or in other words, these two planes  13   a  and  13   b  are discontinuous. The first and second planes  13   a  and  13   b  may have their own two-dimensional shapes, such as triangles and quadrangles. The illustrated second plane  13   b  includes an overlapping area  13   c  and a non-overlapping area  13   d . That is, the overlapping area  13   c  overlaps with the first plane  13   a , while the non-overlapping area  13   d  does not overlaps with the first plane  13   a  or any other plane. Although  FIG. 1  does not depict it, the second plane  13   b  may further include other overlapping areas that overlap with some planes of other elements. In this way, the second plane  13   b  partially overlaps with one or more planes of other elements. The next part will describe how to associate the unknowns between those planes  13   a  and  13   b.    
     The magnetic field simulator apparatus  10  includes a storage unit  11  and a computation unit  12 . The storage unit  11  may be a volatile memory device such as a random access memory (RAM), or may be a non-volatile storage device such as a hard disk drive (HDD) or flash memory. The computation unit  12  may be a central processing unit (CPU), digital signal processor (DSP), or any other processor. The computation unit  12  may also include an application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or any other electronic circuit designed for special purposes. Such processors or circuits are configured to execute a magnetic field simulator program loaded on a memory (e.g., RAM). The term “processor” may be used to refer to a single processing device or a multiprocessor system including two or more processing devices. 
     The storage unit  11  provides a storage space for various data of the model  13 . More particularly, the storage unit  11  stores position data  14   a  and first magnetic field data  14   b . The position data  14   a  includes at least information about the position of the first plane  13   a  noted above. For example, the position data  14   a  describes the position of each vertex or edge of the first plane  13   a , or of the center of gravity of the first plane  13   a . The position data  14   a  may also include such position information for the position of the second plane  13   b . The first magnetic field data  14   b  includes information about a magnetic field in the first plane  13   a . For example, the first magnetic field data  14   b  includes variables defined at each edge of the first plane  13   a . More specifically, the vector potential of such an edge is given as the product of a direction vector along the edge and a coefficient indicating its magnitude. The coefficient is what is to be solved as an unknown, and a variable is thus assigned to the edge to represent the coefficient. 
     The computation unit  12  calculates second magnetic field data  14   c  for the overlapping area  13   c  of the second plane  13   b , based on the position data  14   a  and first magnetic field data  14   b  stored in the storage unit  11 . For example, this second magnetic field data  14   c  describes the magnetic field on surrounding line segments of the overlapping area  13   c , excluding its boundary line with the non-overlapping area  13   d . That is, the second magnetic field data  14   c  includes equations that express unknowns indicating the physical quantity at some line segments on the edges of the second plane  13   b . These equations use variables defined at the edges of the first plane  13   a , and more specifically, they are linear polynomials representing linear combinations of those variables. The unknowns corresponding to the surrounding line segments of the overlapping area  13   c  (except for the boundary line between the overlapping area  13   c  and non-overlapping area  13   d ) are dependent on the unknowns corresponding to edges of the first plane  13   a.    
     The second magnetic field data  14   c  also includes, for example, an equation for the boundary line between the overlapping area  13   c  and non-overlapping area  13   d . This equation expresses an unknown physical value on the boundary line in the form of a linear polynomial of variables defined for edges of the first plane  13   a , similarly to the unknowns on surrounding line segments of the overlapping area  13   c  discussed above. 
     The computation unit  12  then calculates third magnetic field data  14   d  for the non-overlapping area  13   d , based on the second magnetic field data  14   c  calculated above, as well as on the relative position of the non-overlapping area  13   d  with respect to the overlapping area  13   c . This third magnetic field data  14   d  includes, for example, equations that expresses unknown physical values in surrounding line segments of the non-overlapping area  13   d  (i.e., part of the edges of the second plane  13   b ) excluding the boundary line with the overlapping area  13   c . These equations use variables defined at the edges of the first plane  13   a , and more specifically, they are linear polynomials representing linear combinations of those variables. The unknown corresponding to each surrounding line segment of the non-overlapping area  13   d  (excluding the boundary line) is dependent on several unknowns corresponding to edges of the first plane  13   a.    
     For example, the computation unit  12  calculates “contributions” from the boundary line of the non-overlapping area  13   d  to other surrounding line segments of the non-overlapping area  13   d . That is, the computation unit  12  estimates physical quantities at surrounding line segments of the non-overlapping area  13   d  by distributing a physical quantity of the boundary line (which is indicated by the second magnetic field data  14   c ) to other line segments surrounding the non-overlapping area  13   d . The above-noted contribution may depend on the inner product of a direction vector representing the boundary line and a direction vector representing each line segment. For example, the computation unit  12  distributes the physical quantity of the boundary line to a plurality of line segments in proportion to their respective inner products. The contribution thus takes a value of zero for line segments perpendicular to the boundary line, and a larger contribution goes to a line segment facing the boundary line. 
     As can be seen from the above example, each unknown of surrounding line segments of the overlapping area  13   c , as well as of those non-overlapping area  13   d , is expressed as an equation using edge-based variables of the first plane  13   a . The computation unit  12  combines such equations given by the second magnetic field data  14   c  and third magnetic field data  14   d , thus making it possible to express unknowns on all edges of the second plane  13   b  by using edge-based variables the first plane  13   a . Accordingly, every edge-based unknown of the second plane  13   b  can be associated with those of the first plane  13   a  even if the second plane  13   b  has a non-overlapping area that does not overlap with any other element. 
     In operation of the above-described magnetic field simulator apparatus  10  of the first embodiment, second magnetic field data  14   c  is calculated for the overlapping area  13   c  on the basis of position data  14   a  and first magnetic field data  14   b  for a first plane  13   a . Then, on the basis of this second magnetic field data  14   c  and relative positions of the overlapping area  13   c  and non-overlapping area  13   d , third magnetic field data  14   d  is calculated for the non-overlapping area  13   d . The proposed method is capable of obtaining third magnetic field data  14   d  in addition to second magnetic field data  14   c  in this way, even if some moving components in the model  13  move their relative positions and a non-overlapping area  13   d  is consequently produced around their boundary plane. The obtained second and third magnetic field data  14   c  and  14   d  of the second plane  13   b  is not defined independently of, but associated with the first magnetic field data  14   b  describing the first plane  13   a . This means that the second plane  13   b  is entirely associated with the first plane  13   a . The magnetic flux flow between elements having the first plane  13   a  and second plane  13   b  can be expressed properly in the model  13 , which contributes to an increased accuracy of magnetic field simulation with an edge-based FEM. 
     (b) Second Embodiment 
     This section describes a second embodiment. The second embodiment proposes a magnetic field simulator apparatus  100  that analyzes a magnetic field with an edge-based FEM to simulate a distribution of vector potential in a particular object. This magnetic field simulator apparatus  100  may be implemented on a user&#39;s client computer or a server computer. The magnetic field simulator apparatus  100  is a more specific example of the magnetic field simulator apparatus  10  discussed previously in the first embodiment. 
       FIG. 2  is a block diagram illustrating an exemplary hardware configuration of a magnetic field simulator apparatus. The illustrated magnetic field simulator apparatus  100  includes a CPU  101 , a RAM  102 , an HDD  103 , a video signal processing unit  104 , an input signal processing unit  105 , a media reader  106 , and a communication interface  107 . These components are each connected to a bus  108 . 
     The CPU  101  is a processor that includes computational circuits to execute programmed instructions. Specifically, the CPU  101  reads at least part of program and data files stored in the HDD  103  and executes programs after loading them on the RAM  102 . The CPU  101  may include a plurality of processor cores, and the magnetic field simulator apparatus  100  may include two or more processors. These processors or processor cores may be used to execute a plurality of processing operations (described later) in a parallel fashion. The term “processor” may be used to refer to a single processing device or a multiprocessor system including two or more processing devices. 
     The RAM  102  is a volatile semiconductor memory device that temporarily stores programs that the CPU  101  executes, as well as various data objects that the CPU  101  manipulates in the course of computation. Other type of memory devices may be used in place of or together with the RAM  102 , and the magnetic field simulator apparatus  100  may have two or more sets of such memory devices. 
     The HDD  103  serves as a non-volatile storage device to store program and data files of the operating system (OS), middleware, applications, and any other kind of software. A magnetic field simulator program is stored in the HDD  103  as one of those programs. The magnetic field simulator apparatus  100  may include a plurality of non-volatile storage devices such as flash memories and solid state drives (SSD) in place of, or together with the HDD  103 . 
     The video signal processing unit  104  produces video images in accordance with commands from the CPU  101  and outputs them on a screen of a monitor  111  coupled to the magnetic field simulator apparatus  100 . The monitor  111  may be, for example, a cathode ray tube (CRT) display, liquid crystal display (LCD), plasma display panel (PDP), organic electro-luminescence (OEL) display, or other display device. 
     The input signal processing unit  105  receives input signals from input devices  112  and supplies them to the CPU  101 . The input devices  112  include pointing devices (e.g., mouse, touchscreen, touchpad, trackball), keyboards, remote controllers, push button switches, and the like. The magnetic field simulator apparatus  100  allows connection of two or more input devices of different categories. 
     The media reader  106  is a device used to read programs and data stored in a storage medium  113 . The storage media  113  include, for example, magnetic disk media such as flexible disk (FD) and HDD, optical disc media such as compact disc (CD) and digital versatile disc (DVD), magneto-optical discs (MO), and semiconductor memory devices. The media reader  106  transfers programs and data read out of such a storage medium  113  to, for example, the RAM  102  or HDD  103 . 
     The communication interface  107  is connected to a network  114  for communication with remote devices. The communication interface  107  may be designed for a wired network or a wireless network (or both). In the former case, the magnetic field simulator apparatus  100  is connected to a network device (e.g., switch) via a cable. In the latter case, the magnetic field simulator apparatus  100  is linked to a base station or an access point via a radio link. 
     Some of the components seen in  FIG. 2  may be optional. For example, the media reader  106  may be omitted. The video signal processing unit  104  and input signal processing unit  105  may also be omitted in the case where the magnetic field simulator apparatus  100  is implemented as a server computer. It may also be possible to integrate a monitor  111  and input devices  112  into the enclosure of the magnetic field simulator apparatus  100 . It is further noted that the CPU  101  is an example of the computation unit  12  discussed in the first embodiment, and that the RAM  102  or HDD  103  is an example of the storage unit  11  discussed in the same. 
     An example of magnetic field simulation using an edge-based FEM will now be described below. To begin with,  FIGS. 3A and 3B  illustrate examples of unknowns in an edge-based FEM. FEM generally uses a model including nodes, edges, and elements. In the case of the second embodiment, the magnetic field simulator apparatus  100  uses a three-dimensional model including these things. The term “element” in FEM means each small region into which the model space is divided. The term “node” refers to each vertex of an element, and the term “edge” each of the line segments that delineate the element. In other words, an edge connects two nodes. The term “mesh” may also be used to refer to a set of elements or each individual element. 
     The space of a three-dimensional model is divided into multiple elements. The resulting three-dimensional elements may include tetrahedral elements seen in  FIG. 3A  and hexahedral elements seen in  FIG. 3B . Tetrahedral elements are each formed from four triangular planes. Hexahedral elements are each formed from six quadrangular planes. Note that the tetrahedral elements may not be regular tetrahedrons, and the hexahedral elements may not be regular hexahedrons. The magnetic field simulator apparatus  100  can handle various shapes of tetrahedral elements, hexahedral elements, or their combination. 
     As an example, the tetrahedral element  21  in  FIG. 3A  has six edges  21   a ,  21   b ,  21   c ,  21   d ,  21   e , and  21   f . Edges  21   a ,  21   b , and  21   c  form one triangular plane. Edges  21   a ,  21   d , and  21   e  form another triangular plane. Edges  21   b ,  21   e , and  21   f  form yet another triangular plane. Edges  21   c ,  21   d , and  21   f  form still another triangular plane. 
     As another example, the hexahedral element  22  in  FIG. 3B  has twelve edges  22   a ,  22   b ,  22   c ,  22   d ,  22   e ,  22   f ,  22   g ,  22   h ,  22   i ,  22   j ,  22   k , and  22   l . Edges  22   a ,  22   b ,  22   e , and  22   h  form one quadrangular plane. Edges  22   c ,  22   d ,  22   f , and  22   g  form another quadrangular plane. Edges  22   a ,  22   d ,  22   i , and  22   j  form yet another quadrangular plane. Edges  22   b ,  22   c ,  22   k , and  22   l  form still another quadrangular plane. Edges  22   e ,  22   f ,  22   i , and  22   l  form still another quadrangular plane. Edges  22   g ,  22   h ,  22   j , and  22   k  form still another quadrangular plane. 
     The edge-based FEM defines a “basis function” (also called a “basis vector”) along each edge, in the form of a unit vector (i.e., vector with a length of one). The direction of each such basis function is previously selected from two possibilities in the way described below. 
     For the tetrahedral element  21  of  FIG. 3A , basis function N 1  is defined for one edge  21   a . Note that this symbol N 1  represents a vector although no particular vector symbol (e.g., “→”) is attached. Similarly, basis functions N 2 , N 3 , N 4 , N 5 , and N 6  are defined for the other edges  21   b ,  21   c ,  21   d ,  21   e , and  21   f . For the hexahedral element  22  of  FIG. 3B , basis functions N 1 , N 2 , N 3 , N 4 , N 5 , N 6 , N 7 , N 8 , N 9 , N 10 , N 11 , and N 12  are defined for edges  22   a ,  22   b ,  22   c ,  22   d ,  22   e ,  22   f ,  22   g ,  22   h ,  22   i ,  22   j ,  22   k , and  22   l , respectively. 
     The edge-based FEM also defines a variable representing a scalar unknown at each edge. These variables are evaluated through execution of the edge-based FEM. The unknown at a certain edge indicates the magnitude of vector potential of the edge, and it means a coefficient by which the basis function of the edge is multiplied. That is, each edge is given a particular vector potential that is expressed as a basis function multiplied by an unknown. Vector potential A of an element as a whole is then given by combining vector potentials of the element&#39;s surrounding edges (six edges for a tetrahedral element, and twelve edges for a hexahedral element) according to the following equation (1). 
     
       
         
           
             
               
                 
                   
                     A 
                     → 
                   
                   = 
                   
                     
                       ∑ 
                       n 
                     
                      
                     
                         
                     
                      
                     
                       
                         A 
                         n 
                       
                        
                       
                         
                           N 
                           → 
                         
                         n 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     where n is the edge number indicating a surrounding edge of an element, A n  represents a variable assigned to the n-th edge, and N n  represents a basis function of the n-th edge. 
     For example, variables A 1 , A 2 , A 3 , A 4 , A 5 , and A 6  are defined for edges  21   a ,  21   b ,  21   c ,  21   d ,  21   e , and  21   f  of the tetrahedral element  21  of  FIG. 3A . The edges  21   a ,  21   b ,  21   c ,  21   d ,  21   e , and  21   f  have their respective vector potentials expressed as A 1 N 1 , A 2 N 2 , A 3 N 3 , A 4 N 4 , A 5 N 5 , and A 6 N 6 . Vector potential of the tetrahedral element  21  as a whole is then obtained by combining (adding up) these vector potentials into one. For the hexahedral element  22  of  FIG. 3B , variables A 1 , A 2 , A 3 , A 4 , A 5 , A 6 , A 7 , A 8 , A 9 , A 10 , A 11 , and A 12  are defined for its edges  22   a ,  22   b ,  22   c ,  22   d ,  22   e ,  22   f ,  22   g ,  22   h ,  22   i ,  22   j ,  22   k , and  22   l , respectively. The edges  22   a ,  22   b ,  22   c ,  22   d ,  22   e ,  22   f ,  22   g ,  22   h ,  22   i ,  22   j ,  22   k , and  22   l  have their respective vector potentials expressed as A 1 N 1 , A 2 N 2 , A 3 N 3 , A 4 N 4 , A 5 N 5 , A 6 N 6 , A 7 N 7 , A 8 N 8 , A 9 N 9 , A 10 N 10 , A 11 N 11 , and A 12 N 12 . Then the vector potential of the hexahedral element  22  as a whole is obtained by combining these vector potentials. 
     The magnetic field simulator apparatus  100  calculates variables of individual edges by solving the following magnetic field equation (2) in the above-described model. 
     
       
         
           
             
               
                 
                   
                     
                       σ 
                        
                       
                         
                           ∂ 
                           
                             A 
                             → 
                           
                         
                         
                           ∂ 
                           t 
                         
                       
                     
                     + 
                     
                       
                         ∇ 
                         → 
                       
                        
                       
                         × 
                         
                           ( 
                           
                             
                               1 
                               μ 
                             
                              
                             
                               
                                 ∇ 
                                 → 
                               
                                
                               
                                 × 
                                 
                                   A 
                                   → 
                                 
                               
                             
                           
                           ) 
                         
                       
                     
                   
                   = 
                   
                     
                       J 
                       → 
                     
                     + 
                     
                       
                         1 
                         
                           μ 
                           0 
                         
                       
                        
                       
                         
                           ∇ 
                           → 
                         
                          
                         
                           × 
                           
                             M 
                             → 
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
     where σ represents dielectric constant, μ represents permeability, μ 0  represents permeability in a vacuum, J represents a current density vector, and M represents a magnetization vector of a magnet. The magnetic field simulator apparatus  100  then obtains magnetic flux densities B from the vector potential A by using equation (3). 
         {right arrow over (B)}={right arrow over (∇)}×{right arrow over (A)}   (3)
 
     The magnetic field simulator apparatus  100  can simulate how the vector potential distribution varies with time-dependent relative positions of components of the object under analysis. In this course, the magnetic field simulator apparatus  100  calculates vector potential distribution at two distinct time points, without reforming the element set. However, some adjacent elements located at a boundary of components may lose their continuity because of their positional displacement and consequent loss of shared edges. 
       FIG. 4  illustrates an exemplary model of an electric motor. The illustrated electric motor (or simply “motor”)  30  of  FIG. 4  is an example of an object under magnetic field analysis. The motor  30  includes a stator  31  and a rotor  32 . The rotor  32  has a cylindrical shape and rotates around the longitudinal axis of the cylinder. The stator  31  is a stationary portion of the motor  30  that surrounds the rotor  32 . 
     Suppose that the geometry of the motor  30  at a certain time point is divided into a plurality of elements. The produced elements include adjacent elements in a boundary region between the stator  31  and rotor  32 , and these adjacent elements share some edges on the boundary plane. This means that those boundary elements of the stator  31  are continuous with those of the rotor  32 . Referring to the example of  FIG. 4 , one element  31   a  of the stator  31  is adjacent to one element  32   a  of the rotor  32 . These two elements  31   a  and  32   a  share an edge on the boundary plane and are thus deemed continuous. Likewise, another element  31   b  of the stator  31  is adjacent to another element  32   b  of the rotor  32 . These two elements  31   b  and  32   b  also share an edge on the boundary plane and are thus deemed continuous. 
       FIG. 5  illustrates an exemplary model of an electric motor that has rotated. As described above, the motor  30  has been modeled as a set of divided elements, and a rotary motion of the rotor  32  relative to the stator  31  causes a displacement of adjacent elements located in their boundary. This displacement brings about discontinuity of the adjacent elements because they are unable to share their boundary edges in that displaced state. Referring to the example of  FIG. 5 , one element  31   a  of the stator  31  is located immediately next to two elements  32   a  and  32   b  of the rotor  32 , with the boundary plane in between. The former element  31   a , however, does not wholly share its boundary edge with either of the latter elements  32   a  and  32   b  and is discontinuous with them. Likewise, another elements  31   b  of the stator  31  is located immediately next to two elements  32   a  and  32   b  of the rotor  32 , with the boundary plane in between. The former element  31   b  also does not wholly share its boundary edge with either of the latter elements  32   a  and  32   b  and is discontinuous with them. 
     Think of two such discontinuous elements on the opposite sides of the boundary plane. If variables are defined at the edges of one element independently of variables of the other element, these variables in the model would not be able to properly represent a flow of magnetic flux between the elements, and the accuracy of magnetic field analysis could consequently be degraded. The proposed magnetic field simulator apparatus  100  overcomes this difficulty by expressing unknowns on one side as a linear polynomial of variables on the other side. In other words, unknowns on one side are made dependent on unknowns on the other side of the boundary plane. This technique associates the former unknowns with the latter unknowns, thus enabling more accurate representation of flux flows between boundary elements. The magnetic field simulator apparatus  100  therefore continues the magnetic field analysis with the same model although it now contains discontinuous elements. Here the planes located on the boundary are divided into two groups called “master planes” and “slave planes.” Master planes are the planes whose edges are assigned independent variables. Slave planes are the planes whose unknowns are dependent on the variables of master planes. That is, no independent variables are defined for the slave planes. 
       FIG. 6  illustrates an example of master-side and slave-side elements. This example assumes that the foregoing element  21  of  FIG. 3A  is located next to another tetrahedral element  23  having edges  23   a ,  23   b ,  23   c ,  23   d ,  23   e , and  23   f . Regarding the latter element  23 , edges  23   a ,  23   b , and  23   c  form a triangular plane. Likewise, edges  23   a ,  23   d , and  23   e  form another triangular plane, edges  23   b ,  23   e , and  23   f  form yet another triangular plane, and edges  23   c ,  23   d , and  23   f  form still another triangular plane. The top plane of the lower element  23  (i.e., the plane formed from edges  23   a ,  23   b , and  23   c ) is partly in contact with the bottom plane of the upper element  21  (i.e., the one formed from edges  21   a ,  21   b , and  21   c ). These two planes, however, do not share any of their edges, and thus the elements  21  and  23  are discontinuous. 
     Basis functions N 7 , N 8 , and N 9  and variables A 7 , A 8 , and A 9  are defined at edges  23   d ,  23   e ,  23   f  of the lower element  23 . That is, these edges  23   d ,  23   e , and  23   f  have their vector potentials A 7 N 7 , A 8 N 8 , and A 9 N 9 . In contrast, basis functions N s   2 , N s   2 , and N s   3  and variables A s   1 , A s   2 , and A s   3  are defined at other edges  23   a ,  23   b , and  23   c  since the plane of these edges is in contact with the upper element  21 . The edges  23   a ,  23   b , and  23   c  have their respective vector potentials A s   2 N s   2 , A s   2 N s   2 , and A s   3 N s   3 . Note that A s   1 , A s   2 , A s   3  are not independent variables, but depend on the other element&#39;s variables A 1 , A 2 , A 3 , and the like. The plane formed by edges  21   a ,  21   b , and  21   c  of the upper element  21  is therefore deemed to be a master plane, while the plane formed by edges  23   a ,  23   b , and  23   c  of the lower element  23  is deemed to be a slave plane. 
     The vector potential of the element  21  as a whole is calculated by adding up those of its six edges  21   a ,  21   b ,  21   c ,  21   d ,  21   e , and  21   f  as seen in equation (4) below. Similarly the vector potential of the element  23  as a whole is calculated by adding up those of its edges  23   a ,  23   b ,  23   c ,  23   d ,  23   e , and  23   f  as seen in equation (5) below. As will be discussed later in detail, each slave-plane variable A s   1 , A s   2 , and A s   3  is to be replaced with a linear polynomial of variables A 1 , A 2 , A 3 , and the like of other elements, so as to express the electro-magnetic continuity between the two elements  21  and  23 . 
         {right arrow over (A)}=A   1   {right arrow over (N)}   1   +A   2   {right arrow over (N)}   2   +A   3   {right arrow over (N)}   3   +A   4   {right arrow over (N)}   4   +A   5   {right arrow over (N)}   5   +A   6   {right arrow over (N)}   6   (4)
 
         {right arrow over (A)}=A   1   s   {right arrow over (N)}   1   s   +A   2   s   {right arrow over (N)}   2   s   +A   3   s   {right arrow over (N)}   3   s   +A   7   {right arrow over (N)}   7   +A   8   {right arrow over (N)}   8   +A   9   {right arrow over (N)}   9   (5)
 
       FIG. 7A to 7D  illustrate various combinations of master-plane and slave-plane shapes. It is supposed now that the magnetic field simulator apparatus  100  uses tetrahedral elements formed from triangular planes as well as hexahedral elements formed from quadrangular planes. In this case, the overlapping combinations of a master plane and a slave plane are categorized into four patterns described below. Referring to the first pattern in  FIG. 7A , a triangular slave plane  25   a  partly overlaps with a triangular master plane  24   a . Referring to the second pattern in  FIG. 7B , a quadrangular slave plane  25   b  partly overlaps with a quadrangular master plane  24   b . Referring to the third pattern in  FIG. 7C , a quadrangular slave plane  25   c  partly overlaps with a triangular master plane  24   c . Referring to the fourth pattern in  FIG. 7D , a triangular slave plane  25   d  partly overlaps with a quadrangular master plane  24   d.    
     The following description mainly assumes the first pattern of master and slave planes (i.e., both are triangular planes) to demonstrate the proposed calculation. The same calculation policy may also apply to the second to fourth patterns. 
       FIG. 8  illustrates a first exemplary overlap of a slave plane with master planes. In this example, one slave plane  42   a  overlaps with six master planes  41   a ,  41   b ,  41   c ,  41   d ,  41   e , and  41   f , which may respectively be referred to as first to sixth master planes. The individual master planes  41   a ,  41   b ,  41   c ,  41   d ,  41   e , and  41   f  and slave plane  42   a  belong to different elements. As seen in  FIG. 8 , the first master plane  41   a  contacts with the second master plane  41   b  at one shared edge. The second master plane  41   b  contacts with the third master plane  41   c  at one shared edge. The third master plane  41   c  contacts with the fourth master plane  41   d  at one shared edge. The fourth master plane  41   d  contacts with the fifth master plane  41   e  at one shared edge. The fifth master plane  41   e  contacts with the sixth master plane  41   f  at one shared edge. The sixth master plane  41   f  contacts with the first master plane  41   a  at one shared edge. 
     The slave plane  42   a  partly overlaps with each of the master planes  41   a ,  41   b ,  41   c ,  41   d ,  41   e , and  41   f . That is, the slave plane  42   a  is divided into six separate regions that respectively overlap with the master planes  41   a ,  41   b ,  41   c ,  41   d ,  41   e , and  41   f . The slave plane  42   a  does not have a non-overlapping area. 
     The first master plane  41   a  is surrounded by three edges with their respective basis functions N m   1 , N m   2 , and N m   12 . The second master plane  41   b  is surrounded by three edges with their respective basis functions N m   2 , N m   3 , and N m   4 . The third master plane  41   c  is surrounded by three edges with their respective basis functions N m   4 , N m   5 , and N m   6 . The fourth master plane  41   d  is surrounded by three edges with their respective basis functions N m   6 , N m   7 , and N m   8 . The fifth master plane  41   e  is surrounded by three edges with their respective basis functions N m   8 , N m   9 , and N m   10 . The sixth master plane  41   f  is surrounded by three edges with their respective basis functions N m   10 , N m   11 , and N m   12 . Independent variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , A m   7 , A m   8 , A m   9 , A m   10 , A m   11 , and A m   12  are defined for different edges indicated by the basis functions N m   1 , N m   2 , N m   3 , N m   4 , N m   5 , N m   6 , N m   7 , N m   8 , N m   9 , N m   10 , N m   11 , and N m   12 . These variables represent unknowns to be solved by the magnetic field simulator apparatus  100 . 
     The slave plane  42   a , on the other hand, is surrounded by edges with basis functions N s   1 , N s   2 , and N s   3 . Variables A s   1 , A s   2 , and A s   3  are defined for different edges indicated by the basis functions N s   1 , N s   2 , and N s   3 . These variables A s   1 , A s   2 , and A s   3  are dependent variables, and individually expressed as a linear polynomial of multiple variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , A m   7 , A m   8 , A m   9 , A m   10 , A m   11 , and A m   12  of master planes. 
     The conservation law of magnetic flux may be used to obtain a relationship between master-plane variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , A m   7 , A m   8 , A m   9 , A m   10 , A m   11 , and A m   12  and slave-plane variables A s   1 , A s   2 , and A s   3 . Specifically, magnetic flux Φ is calculated as a surface integral of magnetic flux density B as seen in equation (6). Magnetic flux density B is calculated as a line integral of vector potential A. 
       ∫ s   {right arrow over (B)}d{right arrow over (S)}=∫   s ({right arrow over (Λ)}×{right arrow over ( A )}) {right arrow over (n)}dS=     {right arrow over (A)}d{right arrow over (l)}=Φ   (6)
 
     where dS is a small surface for integration, and n is a normal vector of that surface. 
     The unknown at an edge of the slave plane  42   a  can be obtained as a line integral of vector potential along the edge over its overlapping master planes. To express such line integrals, several line vectors are defined on each edge of the slave plane  42   a  as will be described below. 
     That is, a first line vector l s   1  is defined to indicate the whole edge of basis function N s   1  in the slave plane  42   a . Similarly, a second line vector l s   2  is defined to indicate the whole edge of basis function N s   2 , and a third line vector l s   3  is defined to indicate the whole edge of basis function N s   3 . The first line vector l s   1  is then divided into smaller line vectors as follows: l m6   1  representing a line segment on the sixth master plane  41   f , l m1   1  representing a line segment on the first master plane  41   a , and l m2   1  representing a line segment on the second master plane  41   b . Similarly, the second line vector l s   2  is divided into smaller line vectors as follows: l m2   2  representing a line segment on the second master plane  41   b , l m3   2  representing a line segment on the third master plane  41   c , and l m4   2  representing a line segment on the fourth master plane  41   d . The third line vector l s   3  is also divided into smaller line vectors as follows: l m4   3  representing a line segment on the fourth master plane  41   d , l m5   3  representing a line segment on the fifth master plane  41   e , and l m6   3  representing a line segment on the sixth master plane  41   f.    
     Line vectors have been defined in the way described above. The unknown value of variable A s   1  is now obtained by line-integrating the master-plane vector potentials along line vector l s   1 . This line integral along l s   1  can be divided into three line integrals along the following divided line vectors: l m6   1  on the sixth master plane  41   f , l m1   1  on the first master plane  41   a , and l m2   1  on the second master plane  41   b . Here, the vector potential in the sixth master plane  41   f  is given as a combination of vector potentials of edges indicated by basis functions N m   10 , N m   11 , and N m   12 . Similarly, the vector potential in the first master plane  41   a  is given as a combination of vector potentials of edges indicated by basis functions N m   2 , N m   2 , and N m   12 . The vector potential in the second master plane  41   b  is given as a combination of vector potentials of edges indicated by basis functions N m   2 , N m   3 , and N m   4 . Accordingly, the unknown variable A s   1  in question is calculated as in equation (7) below. As seen from this equation (7), variable A s   1  of the slave plane  42   a  can be replaced with a linear polynomial of multiple variables A m   1 , A m   2 , A m   3 , A m   4 , A m   10 , A m   11 , and A m   12 . Note that the inner product of each basis function and foregoing line vector has a specific numerical value since the coordinates of each node are known. 
     
       
         
           
             ( 
             7 
             ) 
           
         
       
       
         
           
             
               
                 
                   
                     ∫ 
                     
                       
                         A 
                         → 
                       
                        
                       
                          
                         
                           
                             l 
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                             s 
                           
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                   = 
                     
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                       1 
                       s 
                     
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                             N 
                             → 
                           
                           1 
                           s 
                         
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                               l 
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                             1 
                             s 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
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                         A 
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                             10 
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                               1 
                               
                                 
                                     
                                 
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                                   6 
                                 
                               
                             
                           
                         
                       
                     
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                               → 
                             
                             11 
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                                   6 
                                 
                               
                             
                           
                         
                       
                     
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                               1 
                               
                                 
                                     
                                 
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                         m 
                       
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                               → 
                             
                             2 
                             m 
                           
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                                 l 
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                               1 
                               
                                 
                                     
                                 
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                                   m 
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                             12 
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                                 l 
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                               1 
                               
                                 
                                     
                                 
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                                   1 
                                 
                               
                             
                           
                         
                       
                     
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                         A 
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                         m 
                       
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                               → 
                             
                             2 
                             m 
                           
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                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
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                                   m 
                                    
                                   
                                       
                                   
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                                   2 
                                 
                               
                             
                           
                         
                       
                     
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                         m 
                       
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                               N 
                               → 
                             
                             3 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         4 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             4 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     Similarly, the unknown value of variable A s   2  is obtained by line-integrating the master-plane vector potentials along line vector l s   2 . This line integral along l s   2  can be divided into three line integrals along the following divided line vectors: l m2   2  on the second master plane  41   b , l m3   2  on the third master plane  41   c , and l m4   2  on the fourth master plane  41   d . Accordingly, the unknown variable A s   2  in question is calculated as in equation (8) below. This means that variable A s   2  of the slave plane  42   a  can be replaced with a linear polynomial of multiple variables A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , A m   7 , and A m   8 . 
     
       
         
           
             ( 
             8 
             ) 
           
         
       
       
         
           
             
               
                 
                   
                     ∫ 
                     
                       
                         A 
                         → 
                       
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                          
                         
                           
                             l 
                             2 
                             s 
                           
                           → 
                         
                       
                     
                   
                   = 
                     
                    
                   
                     
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                       2 
                       s 
                     
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                             → 
                           
                           2 
                           s 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             2 
                             s 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
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                     A 
                     2 
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                               → 
                             
                             3 
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                                   m 
                                    
                                   
                                       
                                   
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                             4 
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                         m 
                       
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                         m 
                       
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                                    
                                   
                                       
                                   
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                                   3 
                                 
                               
                             
                           
                         
                       
                     
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                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
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                               → 
                             
                             6 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
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                                   m 
                                    
                                   
                                       
                                   
                                    
                                   3 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     
                       
                         A 
                         6 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             6 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         7 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             7 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         8 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             8 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     Further, the unknown value of variable A s   3  is obtained by line-integrating the master-plane vector potentials along line vector l s   3 . This line integral along l s   3  can be divided into three line integrals along the following divided line vectors: l m4   3  on the fourth master plane  41   d , l m5   3  on the fifth master plane  41   e , and l m6   3  on the sixth master plane  41   f . Accordingly, the unknown variable A s   3  in question is calculated as in equation (9) below. This means that variable A s   3  of the slave plane  42   a  can be replaced with a linear polynomial of multiple variables A m   6 , A m   7 , A m   8 , A m   9 , A m   10 , A m   11 , and A m   12 . 
     
       
         
           
             ( 
             9 
             ) 
           
         
       
       
         
           
             
               
                 
                   
                     ∫ 
                     
                       
                         A 
                         → 
                       
                        
                       
                          
                         
                           
                             l 
                             3 
                             s 
                           
                           → 
                         
                       
                     
                   
                   = 
                     
                    
                   
                     
                       A 
                       3 
                       s 
                     
                      
                     
                       ∫ 
                       
                         
                           
                             N 
                             → 
                           
                           3 
                           s 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             3 
                             s 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     A 
                     3 
                     s 
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         A 
                         6 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             6 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         7 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             7 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         8 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             8 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   4 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     
                       
                         A 
                         8 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             8 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   5 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         9 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             9 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   5 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         10 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             10 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   5 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     
                       
                         A 
                         10 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             10 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   6 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         11 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             11 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   6 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         12 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             12 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   6 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
     
     The above three equations (7), (8), and (9) for slave-plane variables may be generalized into equation (10) seen below. 
     
       
         
           
             
               
                 
                   
                     A 
                     n 
                     s 
                   
                   = 
                   
                     
                       ∑ 
                       i 
                     
                      
                     
                         
                     
                      
                     
                       
                         ∑ 
                         j 
                       
                        
                       
                           
                       
                        
                       
                         
                           A 
                           j 
                           m 
                         
                          
                         
                           
                             N 
                             → 
                           
                           j 
                           m 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             n 
                             
                               
                                   
                               
                                
                               mi 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     where n is the edge number indicating a specific edge of the slave plane, i is the plane number indicating a specific master plane that overlaps with the slave plane in question, and j is the edge number of a specific edge of the i-th master plane. A s   n  represents the n-th edge variable of the slave plane. A m   j  represents the j-th edge variable of the i-th master plane. N m   j  is a basis function that indicates the j-th edge of the i-th master plane. l mi   n  is a line vector representing a line segment that is a part of the n-th edge of the slave plane and overlaps with the i-th master plane. Equation (10) associates unknowns on the slave plane with unknowns on its overlapping master planes and thus enables calculation of the former unknowns once the latter unknowns are solved. 
     Unknowns at the edges of a slave plane can be calculated with equations (7), (8), (9), and (10) described above when the entire slave plane overlap with one or more master planes. These equations (7), (8), (9), and (10) may, however, not be applied as is to the case in which the slave place further has a non-overlapping area against any of its master planes, because it is not possible to simply line-integrate vector potentials for a part of the slave-plane edges. The next part of the description will now go into details of how unknowns are calculated in such cases. 
       FIG. 9  illustrates a second exemplary overlap of a slave plane with master planes. Here a slave plane  44   a  is partly overlaps with first to third master planes  43   a ,  43   b , and  43   c . The individual master planes  43   a ,  43   b , and  43   c  and slave plane  44   a  belong to different elements. The first master plane  43   a  contacts with the second master plane  43   b  at one shared edge. The second master plane  43   b  contacts with the third master plane  43   c  at one shared edge. The slave plane  44   a  overlaps with each of those master planes  43   a ,  43   b , and  43   c . That is, the slave plane  44   a  includes three regions respectively overlapping with the individual master planes  43   a ,  43   b , and  43   c . The slave plane  44   a  also has a non-overlapping region that is shared with neither of those master planes  43   a ,  43   b , and  43   c  nor any other plane. 
     The first master plane  43   a  is surrounded by edges with basis functions N m   1 , N m   2 , and N m   3 . The second master plane  43   b  is surrounded by edges with basis functions N m   2 , N m   4 , and N m   5 . The third master plane  43   c  is surrounded by edges with basis functions N m   5 , N m   6 , and N m   7 . Independent variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , and A m   7  are defined for different edges indicated by the basis functions N m   1 , N m   2 , N m   3 , N m   4 , N m   5 , N m   6 , and N m   7 . These variables represent unknowns to be solved by the magnetic field simulator apparatus  100 . The slave plane  44   a , on the other hand, is surrounded by edges with basis functions N s   1 , N s   2 , and N s   3 , and variables A s   1 , A s   2 , and A s   3  are defined for different edges indicated by the basis functions N s   1 , N s   2 , and N s   3 . These variables A s   1 , A s   2 , and A s   3  are dependent variables and individually expressed as a linear polynomial of multiple variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , and A m   7  of master planes. 
     Line vectors are defined over the edges of the slave plane  44   a  similarly to the case of  FIG. 8 . That is, a first line vector l s   1  is defined to indicate the whole edge of basis function N s   1  in the slave plane  44   a . Likewise, a second line vector l s   2  is defined to indicate the whole edge of basis function N s   2 , and a third line vector l s   3  is defined to indicate the whole edge of basis function N s   3 . 
     Referring now to the overlapping area (hatched in  FIG. 9 ) of the slave plane  44   a  and master planes  43   a ,  43   b , and  43   c , more line vectors are defined along its surrounding line segments in the way described below. What is defined on the edge of line vector l s   1  is a line vector l m1   1  overlapping with the first master plane  43   a  and another line vector l m2   1  overlapping with the second master plane  43   b . What is defined on the edge of line vector l s   2  is a line vector l m2   2  overlapping with the second master plane  43   b  and another line vector l m3   2  overlapping with the third master plane  43   c.    
     A boundary line  44   b  is also drawn to demarcate the overlapping area from the non-overlapping area of the slave plane  44   a . What is defined on this boundary line  44   b  is a line vector l s1   3  overlapping with an edge of the first master plane  43   a  and another line vector l s1   7  overlapping with an edge of the third master plane  43   c.    
     The above-defined line vectors are used to calculate vector potentials for the overlapping area of the slave plane  44   a . That is, the vector potential of each line segment that overlaps with one master plane is obtained by line-integrating vector potentials of the overlapping master plane along a line vector corresponding to that line segment. This calculation method, however, does not readily work for the remaining line segments of the slave plane  44   a  because they have no overlap with the master planes  43   a ,  43   b , and  43   c  and thus receive no direct effects from them. One thing to note here is that the boundary line  44   b  provides some “contribution” to the vector potentials in those non-overlapping line segments of the slave plane  44   a.    
     Equation (11) for unknown variable A s   1  includes line integrals along line vector l m1   1  over the first master plane  43   a  and line integrals along line vector l m2   1  over the second master plane  43   b . Also included is a contribution term (expressed as a new variable A s*   1 ) from the boundary line  44   b  to the non-overlapping part of line vector l s   1 . The sum of these line integrals and contribution term gives the unknown value of A s   1 . The vector potential in the first master plane  43   a  is given as a combination of vector potentials of edges indicated by basis functions N m   1 , N m   2 , and N m   3 . The vector potential in the second master plane  43   b  is given as a combination of vector potentials of edges indicated by basis functions N m   2 , N m   4 , and N m   5 . 
     
       
         
           
             ( 
             11 
             ) 
           
         
       
       
         
           
             
               
                 
                   
                     ∫ 
                     
                       
                         A 
                         → 
                       
                        
                       
                          
                         
                           
                             l 
                             1 
                             s 
                           
                           → 
                         
                       
                     
                   
                   = 
                     
                    
                   
                     
                       A 
                       1 
                       s 
                     
                      
                     
                       ∫ 
                       
                         
                           
                             N 
                             → 
                           
                           1 
                           s 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             1 
                             s 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     A 
                     1 
                     s 
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         A 
                         1 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             1 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         2 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         3 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             3 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     
                       
                         A 
                         2 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         4 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             4 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         5 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             5 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     A 
                     1 
                     
                       s 
                       * 
                     
                   
                 
               
             
           
         
       
     
     Equation (12) for unknown variable A s   2  includes line integrals along line vector l m2   2  over the second master plane  43   b  and line integrals along line vector l m3   2  over the third master plane  43   c . Also included is a contribution term (expressed as a new variable A s*   2 ) from the boundary line  44   b  to the non-overlapping part of line vector l s   2 . The sum of these line integrals and contribution term gives the unknown value of A s   2 . The vector potential in the second master plane  43   b  is given as a combination of vector potentials of edges represented by basis functions N m   2 , N m   4 , and N m   5 . The vector potential in the third master plane  43   c  is given as a combination of vector potentials of edges represented by basis functions N m   5 , N m   6 , and N m   7 . 
     
       
         
           
             ( 
             12 
             ) 
           
         
       
       
         
           
             
               
                 
                   
                     ∫ 
                     
                       
                         A 
                         → 
                       
                        
                       
                          
                         
                           
                             l 
                             2 
                             s 
                           
                           → 
                         
                       
                     
                   
                   = 
                     
                    
                   
                     
                       A 
                       2 
                       s 
                     
                      
                     
                       ∫ 
                       
                         
                           
                             N 
                             → 
                           
                           2 
                           s 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             2 
                             s 
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     A 
                     2 
                     s 
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         A 
                         2 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         4 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             4 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         5 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             5 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     
                       
                         A 
                         5 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             5 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   3 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         6 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             6 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   3 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         7 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             7 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   3 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     A 
                     2 
                     
                       s 
                       * 
                     
                   
                 
               
             
           
         
       
     
     Unlike the above two edges of the slave plane  44   a , the topmost edge with basis function N s   3  is not directly affected by the master planes  43   a ,  43   b , and  43   c  in terms of vector potential. Equation (13) for this edge thus includes only a contribution term from the boundary line  44   b . That is, the unknown variable A s   3  is expressed by a contribution term alone (expressed as a new variable A s*   3 ) from the boundary line  44   b  to the entire edge of line vector l s   3  as seen in equation (13). 
       ∫ {right arrow over (A)}d{right arrow over (l)}   3   s   =A   3   s   ∫{right arrow over (N)}   3   s   d{right arrow over (l)}   3   s   =A   3   s   =A   3   s*   (13)
 
     During the course of calculating three unknown variables A s   1 , A s   2 , and A s   3  of the triangular slave plane  44   a , the magnetic field simulator apparatus  100  has to calculate a line integral of vector potentials along the boundary line  44   b  between the overlapping and non-overlapping areas. This line integral is a sum of individual line integrals along two line vectors l s1   3  and l s1   7 . The line integral along the former line vector l s1   3  is calculated using interpolation from unknown variable A m   3  of the first master plane  43   a  in accordance with the length ratio of the pertinent edge line segment (i.e., line vector l s1   3  in question) to the entire edge of basis function N m   3 . The line integral along the latter line vector l s1   7  is similarly calculated with interpolation from unknown variable A m   7  of the third master plane  43   c  in accordance with the length ratio of the pertinent edge line segment (i.e., line vector l s1   7  in question) to the entire edge of basis function N m   7 . 
     The above aside, the line integral along the boundary line  44   b  may also be expressed as a sum of three distributions (referred to as first to third distributions) to a non-overlapping part of the slave plane  44   a  from its surrounding areas. Specifically, the first distribution is from the edge of basis function N s   1 . The second distribution is from the edge of basis function N s   2 . The third distribution is from the edge of basis function N s   3 . More specifically, the first distribution is calculated by multiplying a line integral of basis function N s   1  along the boundary line  44   b  by variable A s*   1 . The second distribution is calculated by multiplying a line integral of basis function N s   2  along the boundary line  44   b  by variable A s*   2 . The third distribution is calculated by multiplying a line integral of basis function N s   3  along the boundary line  44   b  by variable A s*   3 . Each line integral along the boundary line  44   b  is divided into two line integrals, one for line vector l s1   3  and the other for line vector l s1   7 . The following equation (14) is thus obtained for calculation of the noted line integral along the boundary line  44   b . Here the line vector l me  represents a sum of two line vectors l s1   3  and l s1   7 . 
     
       
         
           
             ( 
             14 
             ) 
           
         
       
       
         
           
             
               
                 
                   
                     
                       ∫ 
                       
                         
                           l 
                           3 
                           
                             s 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                         + 
                         
                           l 
                           7 
                           
                             s 
                              
                             
                                 
                             
                              
                             1 
                           
                         
                       
                     
                      
                     
                       
                         A 
                         → 
                       
                        
                       
                          
                         
                           l 
                           → 
                         
                       
                     
                   
                   = 
                     
                    
                   
                     
                       
                         A 
                         3 
                         m 
                       
                        
                       
                         
                            
                           
                             l 
                             3 
                             
                               s 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                            
                         
                         
                            
                           
                             l 
                             3 
                             m 
                           
                            
                         
                       
                     
                     + 
                     
                       
                         A 
                         7 
                         m 
                       
                        
                       
                         
                            
                           
                             l 
                             7 
                             
                               s 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                            
                         
                         
                            
                           
                             l 
                             7 
                             m 
                           
                            
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         A 
                         1 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             1 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         2 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         3 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             3 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               3 
                               
                                 
                                     
                                 
                                  
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                   
                 
               
             
             
               
                 
                     
                    
                   
                     
                       
                         A 
                         1 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             1 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               7 
                               
                                 
                                     
                                 
                                  
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         2 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               7 
                               
                                 
                                     
                                 
                                  
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         3 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             3 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               7 
                               
                                 
                                     
                                 
                                  
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                    
                   
                     
                       
                         A 
                         1 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             1 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               me 
                               
                                   
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         2 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               me 
                               
                                   
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         3 
                         
                           s 
                           * 
                         
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             3 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               me 
                               
                                   
                               
                             
                           
                         
                       
                     
                   
                 
               
             
           
         
       
       
         
           
             
               where 
                
               
                   
               
                
               
                 
                   l 
                   → 
                 
                 me 
                 
                     
                 
               
             
             = 
             
               
                 
                   l 
                   → 
                 
                 3 
                 
                   
                       
                   
                    
                   
                     s 
                      
                     
                         
                     
                      
                     1 
                   
                 
               
               + 
               
                 
                   l 
                   → 
                 
                 7 
                 
                   
                       
                   
                    
                   
                     s 
                      
                     
                         
                     
                      
                     1 
                   
                 
               
             
           
         
       
     
     The following equation (15) for the boundary line integral is then obtained by generalizing the above equation (14). In this equation (15), k is the edge number of a master-plane edge overlapping with the boundary line  44   b , i is the plane number of the slave plane in question, and j is the edge number of a specific edge of the i-th slave plane. Accordingly, A m   k  represents a vector potential of the k-th master-plane edge, and l si   k  represents a line vector indicating a line segment of the slave plane which overlaps with the k-th master-plane edge. A s*   j  represents a contribution from the boundary line  44   b  to the j-th edge of the slave plane. N s   j  represents a basis function of the j-th edge of the slave plane. 
     
       
         
           
             
               
                 
                   
                     
                       ∑ 
                       k 
                     
                      
                     
                         
                     
                      
                     
                       ∫ 
                       
                         
                           
                             A 
                             → 
                           
                           k 
                           m 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             k 
                             
                               
                                   
                               
                                
                               si 
                             
                           
                         
                       
                     
                   
                   = 
                   
                     
                       ∑ 
                       j 
                     
                      
                     
                         
                     
                      
                     
                       ∫ 
                       
                           
                       
                        
                       
                         
                           A 
                           j 
                           
                             s 
                             * 
                           
                         
                          
                         
                           
                             N 
                             → 
                           
                           j 
                           s 
                         
                          
                         
                            
                           
                             
                               l 
                               → 
                             
                             me 
                             
                                 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     The problem at this moment is how to distribute the line integral along the boundary line  44   b  to a plurality of line segments constituting a non-overlapping area of the slave plane  44   a . Since neither of the above two equations (14) and (15) per se provides a unique solution for this problem, it is not possible to express each variable A s*   1 , A s*   2 , and A s*   3  in the form of a linear combination (linear polynomial) of variables A m   3  and A m   7 . For this reason, the following calculation assumes that the contribution from the boundary line  44   b  to each line segment is proportional to a line integral of basis function N s   j  along the boundary line  44   b . Under this assumption, the values of these variables A s*   1 , A s*   2 , and A s*   3  are given by the following equations (16). 
     
       
      
       A 
       1 
       s* 
       =t∫{right arrow over (N)} 
       1 
       s 
       d{right arrow over (l)} 
       me  
      
     
     
       
      
       A 
       2 
       s* 
       =t∫{right arrow over (N)} 
       2 
       s 
       d{right arrow over (l)} 
       me  
      
     
         A   3   s*   =t∫{right arrow over (N)}   3   s   d{right arrow over (l)}   me   (16)
 
     where t is a parameter that serves as a scaling factor for the line integral of basis function N s . 
     Equation (17) is then obtained by assigning equations (16) to equation (14). Parameter t is calculated according to equation (18). This equation (18) is generalized in the same way as equation (15), thus obtaining equation (19) for parameter t. In this equation (19), k is the edge number of a master-plane edge that overlaps with the boundary line  44   b , i is the plane number of the slave plane in question, and j is the edge number of a specific edge of the i-th slave plane, as previously noted for equation (15). 
     
       
         
           
             
               
                 
                   
                     
                       
                         A 
                         3 
                         m 
                       
                        
                       
                         
                            
                           
                             l 
                             3 
                             
                               s 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                            
                         
                         
                            
                           
                             l 
                             3 
                             m 
                           
                            
                         
                       
                     
                     + 
                     
                       
                         A 
                         7 
                         m 
                       
                        
                       
                         
                            
                           
                             l 
                             7 
                             
                               s 
                                
                               
                                   
                               
                                
                               1 
                             
                           
                            
                         
                         
                            
                           
                             l 
                             7 
                             m 
                           
                            
                         
                       
                     
                   
                   = 
                   
                     t 
                      
                     
                       { 
                       
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   1 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   2 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   3 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                       
                       } 
                     
                   
                 
               
               
                 
                   ( 
                   17 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     t 
                     = 
                     
                       
                         
                           
                             A 
                             3 
                             m 
                           
                            
                           
                             
                                
                               
                                 l 
                                 3 
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                                
                             
                             
                                
                               
                                 l 
                                 3 
                                 m 
                               
                                
                             
                           
                         
                         + 
                         
                           
                             A 
                             7 
                             m 
                           
                            
                           
                             
                                
                               
                                 l 
                                 7 
                                 
                                   s 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                                
                             
                             
                                
                               
                                 l 
                                 7 
                                 m 
                               
                                
                             
                           
                         
                       
                       
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   1 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   2 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                         + 
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   3 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   18 
                   ) 
                 
               
             
             
               
                 
                   
                       
                   
                    
                   
                     t 
                     = 
                     
                       
                         
                           ∑ 
                           k 
                         
                          
                         
                             
                         
                          
                         
                           
                             
                               A 
                               → 
                             
                             k 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               k 
                               
                                 
                                     
                                 
                                  
                                 si 
                               
                             
                           
                         
                       
                       
                         
                           ∑ 
                           j 
                         
                          
                         
                             
                         
                          
                         
                           
                             ( 
                             
                               ∫ 
                               
                                 
                                   
                                     N 
                                     → 
                                   
                                   j 
                                   s 
                                 
                                  
                                 
                                    
                                   
                                     
                                       l 
                                       → 
                                     
                                     me 
                                     
                                         
                                     
                                   
                                 
                               
                             
                             ) 
                           
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   19 
                   ) 
                 
               
             
           
         
       
     
     After all, variable A s   1  of the slave plane  44   a  can be expressed as a linear polynomial of master-plane variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , and A m   7  as seen from equation (20) below. Likewise, variable A s   2  of the slave plane  44   a  can be expressed as a linear polynomial of master-plane variables A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , and A m   7  as seen from equation (21) below. Variable A s   3  of the slave plane  44   a  can be expressed as a linear polynomial of master-plane variables A m   3  and A m   7  of pertinent master planes as seen from equation (22) below. Note that parameter t in these equations (20), (21), and (22) is given as a linear polynomial of master-plane variables A m   3  and A m   7  as seen from equation (18). Therefore, each equation (20), (21) and (22) actually includes the terms of variables A m   3  and A m   7 . 
     
       
         
           
             
               
                 
                   
                     A 
                     1 
                     s 
                   
                   = 
                   
                     
                       
                         A 
                         1 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             1 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         2 
                         m 
                       
                        
                       
                           
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         3 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             3 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   1 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         2 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         4 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             4 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         5 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             5 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               1 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       t 
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             1 
                             s 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               me 
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   20 
                   ) 
                 
               
             
             
               
                 
                   
                     A 
                     2 
                     s 
                   
                   = 
                   
                     
                       
                         A 
                         2 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             2 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         4 
                         m 
                       
                        
                       
                           
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             4 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
                                   2 
                                 
                               
                             
                           
                         
                       
                     
                     + 
                     
                       
                         A 
                         5 
                         m 
                       
                        
                       
                         ∫ 
                         
                           
                             
                               N 
                               → 
                             
                             5 
                             m 
                           
                            
                           
                              
                             
                               
                                 l 
                                 → 
                               
                               2 
                               
                                 
                                     
                                 
                                  
                                 
                                   m 
                                    
                                   
                                       
                                   
                                    
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     By generalizing the above equations (20), (21), and (22), the following equation (23) is obtained for unknowns of the slave plane  44   a . 
     
       
         
           
             
               
                 
                   
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     The next description will explain some particular effects of the calculation method of “contributions” discussed above, using a new example of overlapping master and slave planes. In this example, the master planes and slave planes are both quadrangles, and some slave planes have one or more edges running perpendicularly to the boundary line. 
       FIG. 10  illustrates a third exemplary overlap of a slave plane with master planes. First and second master planes  45   a  and  45   b  partly overlap with first to third slave planes  46   a ,  46   b , and  46   c . These master planes  45   a  and  45   b  and slave planes  46   a ,  46   b , and  46   c  belong to different elements, and all of them are quadrangular. The first master plane  45   a  contacts with the second master plane  45   b  in one shared edge. The first slave plane  46   a  contacts with the second slave plane  46   b  in one shared edge. The second slave plane  46   b  also contacts with the third slave plane  46   c  in one shared edge. 
     The first slave plane  46   a  partly overlaps with the first master plane  45   a . In other words, the first slave plane  46   a  is formed from an overlapping area over the first master plane  45   a  and a non-overlapping area that has no overlap with any master plane. The second slave plane  46   b  partly overlaps with both the master planes  45   a  and  45   b . That is, the second slave plane  46   b  is formed from an overlapping area over the first master plane  45   a , another overlapping area over the second master plane  45   b , and a non-overlapping area that has no overlap with any master plane. The third slave plane  46   c  partly overlaps with the second master plane  45   b . That is, the third slave plane  46   c  is formed from an overlapping area over the second master plane  45   b  and a non-overlapping area that has no overlap with any master plane. 
     The first master plane  45   a  is surrounded by edges with basis functions N m   1 , N m   2 , N m   3 , and N m   4 . The second master plane  45   b  is surrounded by edges with basis functions N m   3 , N m   5 , N m   6 , and N m   7 . Independent variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , and A m   7  are defined for different edges indicated by the basis functions N m   1 , N m   2 , N m   3 , N m   4 , N m   5 , N m   6 , and N m   7 . These variables represent unknowns to be solved by the magnetic field simulator apparatus  100 . The second slave plane  46   b  is surrounded by edges with basis functions N s   1 , N s   2 , N s   3 , and N s   4 , and variables A s   1 , A s   2 , A s   3 , and A s   4  are defined for different edges indicated by the basis functions N s   1 , N s   2 , N s   3 , and N s   4 . These slave-plane variables A s   1 , A s   2 , A s   3 , and A s   4  are dependent variables and individually expressed as a linear polynomial of multiple variables A m   1 , A m   2 , A m   3 , A m   4 , A m   5 , A m   6 , and A m   7  of master planes. The following description focuses on the second slave plane  46   b , while omitting discussion about the other slave planes  46   a  and  46   c.    
     A line vector l m   4  is defined to represent the whole edge with basis function N m   4  in the first master plane  45   a . Likewise, another line vector l m   7  is defined to represent the whole edge with basis function N m   7 . The second slave plane  46   b  is divided into an overlapping area and a non-overlapping area by a line segment called a boundary line  46   d . This boundary line  46   d  runs perpendicularly to two edges indicated by basis functions N s   1  and N s   3  of the second slave plane  46   b . The boundary line  46   d  is formed from two line segments. One line segment overlaps with an edge of the first master plane  45   a  and is indicated by a line vector l s2   4 . The other line segment overlaps with an edge of the second master plane  45   b  and is indicated by another line vector l s2   7 . The sum of these line vectors l s2   4  and l s2   7  is referred to as a line vector l me . 
     With the foregoing method, a line integral along the boundary line  46   d  is calculated as in equation (24). This line integral is a sum of individual line integrals along two line vectors l s2   4  and l s2   7 . The line integral along the former line vector l s2   4  is calculated with interpolation of an unknown variable A m   4  of the first master plane  45   a  in accordance with the length ratio of line vector l s2   4  to line vector l m   4 . Likewise, the line integral along the latter line vector l s2   7  is calculated with interpolation of an unknown variable A m   7  of the second master plane  45   b  in accordance with the length ratio of line vector l s2   7  to line vector l m   7 . 
     The line integral along the boundary line  46   d  is also expressed as a sum of three distributions (referred to as first to third distributions) to a non-overlapping part of the second slave plane  46   b  from its surrounding areas. Specifically, the first distribution is from the edge of basis function N s   1 . The second distribution is from the edge of basis function N s   3 . The third distribution is from the edge of basis function N s   4 . More specifically, the first distribution is calculated by multiplying a line integral of basis function N s   1  along the boundary line  46   d  by variable A s*   1 . The second distribution is calculated by multiplying a line integral of basis function N s   3  along the boundary line  46   d  by variable A s*   3 . The third distribution is calculated by multiplying a line integral of basis function N s   4  along the boundary line  46   d  by variable A s*   4 . 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
                             
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     Because the edge of basis function N s   1  is perpendicular to the boundary line  46   d , the inner product between basis function N s   1  and line vector l me  is zero. This is also true for basis function N s   3  and its inner product with line vector l me . Accordingly, the line integral of basis function N s   1  along the boundary line  46   d  is zero, as is the line integral of basis function N s   3 . Equation (25) below indicates this fact. As mentioned before, the value of variable A s*   1 , is supposed to be proportional to such line integrals. Variables A s*   1  and A s*   3  are both zero for this reason. After all, the boundary line  46   d  contributes only to the edge of basis function N s   4 , which runs in parallel with the boundary line  46   d.    
       ∫ {right arrow over (N)}   1   s   d{right arrow over (l)}   me   =∫{right arrow over (N)}   3   s   d{right arrow over (l)}   me =0  (25)
 
     The edge of basis function N s   1  is shared by two slave planes  46   a  and  46   b . If a large contribution was given from the boundary line  46   d  to this edge, it would affect the magnetic flux in the first slave plane  46   a . The edge of basis function N s   3  is shared by two slave planes  46   b  and  46   c . If a large contribution was given from the boundary line  46   d  to this edge, it would affect the magnetic flux on the third slave plane  46   c . The foregoing calculation method is likely to evaluate smaller contributions from the boundary line  46   d  to these perpendicular edges of basis functions N s   1  and N s   3 , in contrast to a larger contribution from the boundary line  46   d  to the parallel edge of basis function N s   4 . In other words, the foregoing calculation method prevents the second slave plane  46   b  from affecting the magnetic flux in its adjacent slave planes  46   a  and  46   c.    
     The description now turns to simulation functions of the magnetic field simulator apparatus  100 .  FIG. 11  is a block diagram illustrating an example of functions implemented in the proposed magnetic field simulator apparatus. This magnetic field simulator apparatus  100  includes a geometrical data storage unit  121 , a weight data storage unit  122 , an equation storage unit  123 , an analysis result storage unit  124 , an element calculation unit  131 , a variable combination unit  132 , an equation generation unit  133 , and a solver unit  134 . The geometrical data storage unit  121 , weight data storage unit  122 , equation storage unit  123 , and analysis result storage unit  124  may be implemented as storage spaces reserved in the RAM  102  or HDD  103 , for example. The element calculation unit  131 , variable combination unit  132 , equation generation unit  133 , and solver unit  134  may be implemented as, for example, program modules to be executed by the CPU  101 . 
     The geometrical data storage unit  121  stores geometrical data that describes the geometry of a model. The model is divided into a plurality of elements. The geometrical data includes data of nodes, edges, and planes to describe the shape and position of each element. The task of dividing the model into elements may be performed previously by the user of the magnetic field simulator apparatus  100  or by the element calculation unit  131 . In the former case, the user produces geometrical data describing each node, edge, and plane of the model and sends it into the geometrical data storage unit  121 . In the latter case, the user produces geometrical data describing the geometry of an object as a whole and sends it into the geometrical data storage unit  121 , and the element calculation unit  131  then follows up this geometrical data by adding node data, edge data, and plane data. 
     The weight data storage unit  122  provides a storage space for weight data that associates unknowns in slave planes with those in master planes. More specifically, the weight data indicates the weight of each variable in linear polynomials representing slave-plane unknowns using master-plane variables. Such weight data is produced by a variable combination unit  132  described later. 
     The equation storage unit  123  provides a storage space for simultaneous equations to be solved for unknowns at element edges. These simultaneous equations are expressed in the form of a coefficient matrix (i.e., an array of coefficients in the equations). Such simultaneous equations are produced by the equation generation unit  133  described later. 
     The analysis result storage unit  124  provides a storage space for result data of an edge-based FEM analysis. The result data includes the value of each edge-based unknown calculated by solving simultaneous equations. Such result data is produced by the solver unit  134  described later. 
     The element calculation unit  131  divides a model into small elements in consideration of its entire shape when the model is stored in the geometrical data storage unit  121  in its original non-divided state. To define the shape and position of an element, the element calculation unit  131  first places nodes, draws edges to connect the nodes, produces each plane from multiple nodes, and determines an element formed from those planes. The elements may take the form of a tetrahedron having triangular surfaces or a hexahedron having quadrangular surfaces. The model of an object may include elements having different shapes depending on which regions of the object they represent. 
     The modeled object may include a movable component, such as the rotor  32  discussed in  FIG. 4 . When this is the case, the element calculation unit  131  implements a movement of the component on the model. Here the user may specify the direction of the movement, as well as a unit distance or angle per movement. 
     The variable combination unit  132  works when the element calculation unit  131  has modified the model with a component movement. In response, the variable combination unit  132  reads the modified model out of the geometrical data storage unit  121  and detects elements that have lost continuity in the boundary plane between a moved region and a stationary region. That is, the variable combination unit  132  determines which adjacent elements on the opposite sides of the boundary plane have lost their shared edges as a result of the movement. When such discontinuous elements are found, the variable combination unit  132  selects their pertinent planes either as master planes or as slave planes. The variable combination unit  132  may perform the selection of master and slave planes on its own policies or according to the user&#39;s commands. Referring to, for example, the model of a motor  30  in  FIG. 4 , pertinent planes of its stator  31  may be selected as master planes and those of its rotor  32  may be selected as slave planes. 
     The variable combination unit  132  also defines variables representing unknowns assigned to each edge of model elements. The unknown at an edge takes a scalar value by which the edge&#39;s basis function is multiplied. In other words, this unknown indicates the magnitude of the vector potential at that edge. The variable combination unit  132  then makes such variables of slave-plane edges dependent on the variables of overlapping master-plane edges. That is, each slave-plane variable is replaced with a linear polynomial of master-plane variables. The variable combination unit  132  produces weight data that indicates the weights (i.e., real number coefficients) of variables in those linear polynomials and stores the produced weight data into the weight data storage unit  122 . 
     The equation generation unit  133  reads out weight data from the weight data storage unit  122  and produces simultaneous equations of the variables that the above variable combination unit  132  has defined for each edge, based on the linear polynomials indicated by the weight data. In this process, the equation generation unit  133  does not express the unknowns of slave-plane edges as independent variables, but treats them as variables dependent upon unknowns of master planes, according to the linear polynomials given by the weight data. The equation generation unit  133  generates a coefficient matrix from a collection of coefficients of the simultaneous equations and sends it to the equation storage unit  123 . Generally the coefficient matrix includes a large number of entries, but many of them have a value of zero (i.e., sparse matrix). 
     The solver unit  134  reads a coefficient matrix out of the equation storage unit  123  and solves the corresponding simultaneous equations by applying various operations to the coefficient matrix. There are known algorithms for this solution. The solver unit  134  calculates the unknown of each edge of elements, thus determining vector potentials of the edges. The unknowns of slave-plane edges are calculated not directly from the simultaneous equations, but from other linear equations containing pertinent master-plane unknowns and their weight data. These master-plane unknowns belong to edges of one or more master planes that overlap with the slave plane in question. The solver unit  134  compiles an analysis result from the calculated unknowns and the like and sends it to the analysis result storage unit  124 . The solver unit  134  may visualize the analysis result and present it on the monitor  111 . For example, a distribution of vector potential may be represented by arrows or color gradations. 
       FIG. 12  illustrates an exemplary structure of geometrical data. What is stored in the illustrated geometrical data storage unit  121  includes point data  141 , edge data  142 , and plane data  143 . The point data  141  gives a set of nodes. The edge data  142  gives a set of edges each defined between a pair of nodes. The plane data  143  gives a set of planes each defined by a plurality of nodes (e.g., three nodes for a tetrahedral element, four nodes for a hexahedral element). 
     More specifically, the point data  141  in  FIG. 12  includes the following data fields: point number, X coordinate, Y coordinate, and Z coordinate. The point number field contains a natural number as an identifier indicating a specific node. The X, Y, and Z coordinate fields indicate the node&#39;s position in the model space. The edge data  142  is formed from the following data fields: edge number, point # 1 , and point # 2 . The edge number field contains a natural number as an identifier indicating a specific edge. The point # 1  and point # 2  fields contain two point numbers to specify the end node positions of a specific edge. The plane data  143  is formed from the following data fields: plane number, point # 1 , point # 2 , point # 3 , and point # 4 . The plane number field contains a natural number as an identifier indicating a specific plane. The point # 1  to point # 4  fields contain four point numbers to specify the corner node positions of a specific plane. The point # 4  field may be empty for tetrahedral elements. Note that this plane data  143  may be modified to use edge numbers in place of point numbers for identifying a plane. 
       FIG. 13  illustrates an exemplary structure of weight data. The weight data storage unit  122  provides a storage space for weight data  144 . This weight data  144  offers linear polynomials for calculating unknowns of slave-plane edges. Specifically, the illustrated weight data  144  is formed from the following data fields: slave edge number, master edge count, master edge number, and weight. 
     The slave edge number field contains an edge number that indicates a specific edge of a slave plane. The master edge count field gives the number of master-plane edges pertinent to the unknown of a slave-plane edge that the slave edge number field indicates. This field indicates how many variables of master planes appear in the linear polynomial. The master edge number field specifies a list of edges of pertinent master planes by using edge numbers, thus indicating which master-plane edges relate to the unknown of a slave-plane edge that the slave edge number field indicates. This field contains as many edge numbers as indicated in the master edge count field. The weight field gives a list of real numbers that serve as coefficients for the variables of pertinent master-plane edges relating to the unknown of a slave-plane edge that the slave edge number field indicates. The weight field contains as many real numbers as indicated by the master edge count field. 
       FIG. 14  is a flowchart illustrating an exemplary procedure for combining variables. In step S 1 , the element calculation unit  131  modifies the model by moving at least a movable component (e.g., rotor  32 ) of the modeled object (e.g., motor  30 ). The variable combination unit  132  then extracts elements located at the boundary between the moved component and stationary components. The variable combination unit  132  further extracts master planes from the elements on one side of the boundary plane and slave planes from the elements on the other side of the same. These master and slave planes belong to the boundary plane. The choice of which side is master may be determined by the variable combination unit  132  itself or may be selected by the user. Preferably, one component may contain either master planes or slave planes, but not both. 
     In step S 2 , the variable combination unit  132  selects one of the slave planes extracted at step S 1 . 
     In step S 3 , the variable combination unit  132  determines whether the selected slave plane contains any area that overlaps with one of the master planes. This test for an overlap of two planes is made by calculating the position of each plane on the basis of the foregoing point data  141  and plane data  143  stored in the geometrical data storage unit  121 . The process advances to step S 4  when the selected slave plane has an overlapping area. Otherwise, the process skips to step S 8 . 
     In step S 4 , the variable combination unit  132  identifies one or more master planes that overlap with the currently selected slave plane. The variable combination unit  132  calculates line integrals of vector potentials in these master planes along individual slave-plane edges that belong to the overlapping area. The edge positions of a slave plane are calculated from the point data  141  and edge data  142  in the geometrical data storage unit  121 . The vector potentials in a master plane are expressed by using a basis function and a variable assigned to each edge of the master plane. The noted line integrals are therefore expressed in linear polynomials of the master-plane variables, and these linear polynomials correspond to the variables of edges of the slave plane when the presence of a non-overlapping area is disregarded. 
     In step S 5 , the variable combination unit  132  determines whether the selected slave plane has an area that does not overlap with any master plane. When the selected slave plane has such a non-overlapping area, the process advances to step S 6 . When the slave plane has no such area, the variable combination unit  132  updates weight data  144  in the weight data storage unit  122  to register the linear polynomials obtained in step S 4 . The process then proceeds to step S 8 . 
     In step S 6 , the variable combination unit  132  calculates a boundary line between the overlapping area and non-overlapping area in the selected slave plane. The variable combination unit  132  then calculates a line integral of master-plane vector potentials along the boundary line and determines, based on this line integral, a contribution from the boundary line to a non-overlapping part of the slave-plane edges. Here the contribution to each non-overlapping line segment is supposed to be proportional to a line integral of the basis function of that segment along the boundary line. The determined contribution is expressed in a linear polynomial of master-plane variables. 
     In step S 7 , the variable combination unit  132  adds the contribution term calculated in step S 6  to the linear polynomial calculated in step S 4  for each edge of the selected slave plane. The resulting linear polynomials correspond to the variables of slave-plane edges when the presence of a non-overlapping area is considered. The unknown of each edge of the selected slave plane is expressed by using variables of the master planes. The variable combination unit  132  thus registers the obtained linear polynomials as new entries of the weight data  144 . 
     In step S 8 , the variable combination unit  132  determines whether all the slave planes extracted at step S 1  have been selected and subjected to the above processing. If so, the variable combining process is terminated. If there is any pending slave plane, then the process returns to step S 2  to continue. 
     According to the second embodiment described above, the proposed magnetic field simulator apparatus  100  executes an edge-based FEM analysis in which a slave plane may partly overlap with master planes. The magnetic field simulator apparatus  100  calculates a linear polynomial representing an unknown on the basis of vector potentials of master planes, for overlapping line segments of the slave-plane edges. For non-overlapping line segments of the slave-plane edges, the magnetic field simulator apparatus  100  calculates a linear polynomial representing a contribution from the boundary between the overlapping area and non-overlapping area of the slave plane. This method makes it possible to properly express the unknown of a whole edge of a slave plane by using variables defined in master planes. 
     Although the slave plane is discontinuous with master planes (i.e., does not share any edge with master planes), a flow of magnetic flux between their respective elements is properly expressed, and this feature leads to an improved accuracy of magnetic field analysis. The slave plane may even include a non-overlapping area that has no master planes to overlap with. The proposed method also serves well for such non-overlapping areas, thus providing the same advantages noted above. The proposed method is helpful in an edge-based FEM analysis for magnetic field of an object made up of multiple components whose relative positions may change (e.g., motors), since it eliminates the need for restructuring elements of the model each time they have new positions. 
     The proposed method calculates vector potentials in consideration of a contribution to a non-overlapping area of a slave plane from its boundary line with an overlapping area. The amount of this contribution depends on where the line segment of interest is located in the non-overlapping area with respect to the boundary line. Specifically, a larger contribution is given to a line segment running in parallel with the boundary line, whereas a smaller contribution is given to a line segment perpendicular to the boundary line. This reduces the effect of contributions from one slave plane to its neighboring slave planes and thus improves the accuracy of magnetic field analysis. It also simplifies edge-based FEM computation, thus reducing the workload of magnetic field analysis. 
     The information processing process discussed in the first embodiment may actually be implemented as a program for a magnetic field simulator apparatus  10 . Similarly, the information processing process discussed above in the second embodiment may be implemented as a program for a magnetic field simulator apparatus  100 . These programs may be stored in a non-transitory computer-readable medium (e.g., storage medium  113  in  FIG. 2 ). For example, the suitable storage media for this purpose include (but are not limited to) magnetic disks, optical discs, magneto-optical discs, and semiconductor memory devices. More specifically, magnetic disk media include FD and HDD. Optical disc media include CD, CD-Recordable (CD-R), CD-Rewritable (CD-RW), DVD, DVD recordable (DVD-R), and DVD rewritable (DVD-RW). A program may be distributed in the form of portable storage media. The program encoded in a portable storage medium may be executed after being copied to some other storage medium (e.g., HDD  103 ). 
     Two embodiments have been discussed above. According to one aspect of the embodiments, the proposed techniques enable a magnetic field simulation of an object even if the object includes components whose relative positions may vary. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.