Patent Publication Number: US-6035314-A

Title: Information processing method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for processing information by using the method for representing rational expression which is effective for solving simultaneous algebraic equations and so on. 
     2. Description of the Related Art 
     Recently, the use of a expression processing system has been practical in order to solve scientific and engineering problems. The high-accuracy in solving simultaneous equations including linear equations is fundamental in the expression processing system which processes expression. Increasing the accuracy is an important factor which improves the performance of the whole system. 
     In the expression processing system, the Grobner basis has been used as a general solver for solving simultaneous algebraic equations. However, sometimes it happens that the resultant coefficient becomes quite large amount. 
     This phenomenon is most pronounced in an equation in which the number of solutions is finite. As a result of this, the calculational volume of Grobner basis becomes so large temporally and spatially. 
     Since the calculational volume becomes so large temporally and spatially, the processing time for information processing using the Grobner basis becomes longer and the rate of occupying memory is increased, with the result that the information processing at high efficiency is impossible. 
     Therefore, the following representation of solutions by rational expressions is considered to be effective in compensating for the drawback. 
     In case of the Grobner basis, the solutions of the equation are represented by: 
     
         f.sub.1 (x.sub.1)=0, x.sub.2 =f.sub.2 (x.sub.1), . . . , x.sub.n =f.sub.n (x.sub.1) 
    
     (all of &#34;f&#34; are polynomial.). 
     In case of the representation of rational expression, the solutions are represented by: 
     f 1  (x 1 )=0, x 2  =g 2  (x 1 )/f&#39; 1  (x 1 ), . . . , x n  =g n  (x 1 )/f&#39; 1  (x 1 ) 
     (all of &#34;f&#39; 1  (x 1 )&#34; are differential of polynomial &#34;f 1  (x 1 )&#34;.). 
     In finding the solutions of the given equation, once f 1  (x 1 )=0 is solved, other variables may be obtained by the substitution. Therefore, the above expressions are considered as the same each other. 
     The advantage of the representation of rational expression is that the coefficient of g i  is almost remarkably smaller than the coefficient of f i . As a result of this, there is a possibility of reducing the time and the memory required for finding g i  as compared with f i . 
     When using the obtained solutions in the information processing, the common difference increases as coefficient becomes greater. To avoid increase in common difference, it is necessary to solve the f 1  (x 1 ) at quite high accuracy. Using the representation of rational expression makes the coefficients smaller i.e. the result will be small value, thereby also making the common difference smaller. At the same time, the calculational load is reduced, thereby speeding up the information processing. 
     A method using the character of the symmetric expressions is proposed as one of methods for finding solutions of this type. In this method, when the number of the solutions is N, a table is made by calculating normal forms of N 2  monomials {Ω k  Ω 1  } relative to the tabulation of N monomials {Ω k  }. On the basis of the table, the trace of powers of matrix is calculated. Finally, f i  and g i  are calculated by forming characteristic polynomials of the matrix. 
     Though the representation of solutions by rational expressions is possible according to the method as mentioned above, there are, in practice, problems as follows. 
     1) When the number N of the solutions is large, the time and memory required for calculating N 2  normal forms are increased. 
     2) While the number of the normal forms to be really calculated can be reduced by various ideas, the time and memory required for calculating the aforementioned table are rapidly increased when N is large. 
     3) Because the order of calculations is important to increase the calculating efficiency, it is difficult that the calculations are made in parallel. 
     4) Furthermore, it is not assured that the resultant solutions represent all of the solutions. 
     SUMMARY OF THE INVENTION 
     The present invention employs the following method in order to overcome the problems 1) through 4) as mentioned above. 
     The present invention is based on the perception that, in calculation of the polynomial having the minimum degree of one variable x 1 , i.e. the minimum polynomial f 1  (x 1 ), based on Grobner basis G 1 , the degree of f 1  (x 1 ) equal to the number of the solutions given by G 1  means that all of the solutions can be represented of rational expressions. That is: 
     1. first of all, the minimum polynomial of x 1  is found to decide whether all of the solutions can be represented by rational expressions or not, 
     2. a table to be required is a normal table of monomials of which the number is N at the most, and 
     3. the solutions can be calculated in such a time as corresponding the to volume of the representation of the solutions by using linear equations. 
     This means that the present invention is defined as follows. The present invention provides a method of processing information wherein, in a model in which restrictions among-parameters are given by simultaneous algebraic equations with integral coefficients, when the simultaneous equations have only a finite number of solutions, zero points of a polynomial set F with integral coefficients, which represents the simultaneous equations and is described in a memory, are represented by rational expressions based on zero points of a one-variable polynomial regarding one variable so that the information is processed using the representation of rational expression. Therefore, the method of processing information of the present invention comprises steps of: 
     1-1. choosing a term order O 1  for facilitating the calculation of the Grobner basis; 
     1-2. calculating the Grobner basis G 1  of F with regard to O 1  ; 
     1-3. calculating the minimum polynomial f 1  (x 1 ) based on G 1 , the minimum polynomial f 1  (x 1 ) being a polynomial having the minimum degree of the variable x 1  ; and 
     1-4. when it is decided that the degree of f 1  (x 1 ) is equal to the number of solutions given from G 1 , 
     1-5. controlling the digital processor to find solutions represented by rational expressions that is, 
     {f 1  (x 1 )=0, x 2  =f 2  (x 1 )/f&#39; 1  (x 1 ), . . . , x n  =f n  (x 1 )/f&#39; 1  (x 1 )} [notes: f&#39; 1  (x 1 ) is differential of f 1  (x 1 ).]. 
     In the present invention, it is decided whether the representation of rational expression is possible or not in the step 1-4, by finding the minimum polynomial in the step 1-3. 
     The minimum polynomial can be obtained in the aforementioned step 2-1˜2-3 by the following steps of: 
     2-1. selecting a prime number p which does not divide any head coefficient of all elements of (G 1 ) and assuming φp as an operation of replacing the coefficient by the remainder regarding the prime number p; 
     2-2. obtaining the minimum polynomial f 1  (x 1 ) of x 1  obtained by φp (G 1 ), regarding p as the modulus; 
     2-3. obtaining a one-variable polynomial f 1  (x 1 ) in which the degree is equal to f 1  by replacing the coefficients of f 1  (x 1 ) by undetermined coefficients to calculate normal forms given by G 1  and eliminating the coefficients to solve linear equations with regard to the undetermined coefficients; 
     2-4. when the one-variable polynomial f 1  (x 1 ) is not obtained, repeating the steps 2-2 and 2-3 with replacing p to obtain the minimum polynomial of x 1 . 
     The representation of solutions by rational expressions can be obtained in the aforementioned step 3-1˜3-5 by the following steps of: 
     3-1. selecting a prime number p which does not divide any head coefficient of all elements of (G 1 ) and assuming (p as an operation of replacing the coefficient by the remainder regarding the prime number p; 
     3-2. calculating Grobner basis G 2  with regard to the lexicographical order of φp (G 1 ); 
     3-3. obtaining a one-variable polynomial f 1  (x 1 ) by calculating normal forms given by G 1  of difference between f&#39; 1  (x 1 ) x i  and the normal form of f&#39; 1  (x 1 ) x i  given by G 2  in which the coefficients are replaced by undetermined coefficients in given by G 1  for every i (i=2, . . . , n) and eliminating the coefficients to solve linear equations with the undermined coefficients; 
     3-4. returning a rational expression: {f 1  (x 1 )=0, x 2  =f 2  (x 1 )/f&#39; 1  (x 1 ), . . . , x n  =f n  (x 1 )/f&#39; 1  (x 1 )} as the solutions; and 
     3-5. repeating steps 3-2 through 3-4 re-selecting p selected in the step 3-1 when any one of the linear equations can not be solved. 
     The method of the present invention can be processed by a parallel computer. In this case, the each of f i  are simultaneously obtained by different processors. 
     &lt;When Representation of Rational Expressions is Impossible&gt; 
     As mentioned above, the present invention is characterized in that it is decided whether the representation of rational expression is possible or not in the step 1-4, by finding the minimum polynomial in the step 1-3. On the other hand, there is a problem of processing in case where the degree of f 1  (x 1 ) is not equal to the number of the solutions given by G 1  as a result of finding the minimum polynomial in the step 1-3. 
     In this case, the method further comprises steps of: 
     5-1. selecting a prime number p which does not divide any head coefficient of all elements of (G 1 ) and assuming φp as an operation of replacing the coefficient by the remainder regarding the prime number p; 
     5-2. calculating Grobner basis G 2  with regard to the term order O of φp (G 1 ); 
     5-3. finding an integral coefficient polynomial f h  for each element h of G 2  of which the head coefficient is not divisible by p and the number of head terms coincide with the domain of h; 
     5-4. when the integral coefficient polynomials f h  are found for all of the elements h of G 2 , outputting the whole of f h  as Grobner basis of the integral polynomial set F with regard to the term order O; and 
     5-5. when any one of the integral coefficient polynomials f h  is not found, re-selecting p selected in said step 5-1 and controlling the digital processor to repeat the steps 5-2 through 5-4 to generate the Grobner basis. 
     By using the method as mentioned above, the preparation of a plurality of medium-grade term orders relative to a term order O (assuming O 1 , O 2 , . . . , O n  =O) and the exchange of bases O 1  →O 2 , O 2  →O 3 , . . . , O n-1  →O n  are executed. f h  in the step 5-3 can be found in a candidate generating method by trace-lifting comprising steps of: 
     7-1. first of all, calculating Grobner basis in the modulus p; 
     7-2. storing a history about members and terms in which the elimination was executed and pairs normalized to O, during normalizing φ(P) in this process; 
     7-3. calculating the Grobner basis on rational number based on the history of the foregoing paragraph, at this stage, not executing the normalization on the rational number in relation to the pairs normalized to O in the modulus p, but executing the normalization on the rational number based on the history in relation to pairs normalized to polynomial which is not O in the modulus p, 
     7-4. returning &#34;nil&#34; assuming that the method of selecting p is not appropriate, when the normalization on the rational number does not correspond to the normalization in the modulus p. f h  in the step 5-3 can be found by replacing coefficients of elements of G 2  by undetermined coefficients to calculate normal forms given by G 1  and eliminating the coefficients to solve linear equations with regard to the undetermined coefficients. 
     According to the present invention, the use of the representation of rational expression makes the coefficients smaller, thereby speeding up the calculation and thus reducing the required memory. Since it is previously decided whether the representation of rational expression is possible or not, the reliability of solutions becomes higher and, even when the representation of rational expression is impossible, the most suitable solutions can be obtained, thereby smoothing and speeding up the whole process. 
     &lt;Program&gt; 
     The present invention is executed by a program. This program is stored in a storage medium and then installed in an information processing unit so that the program is executed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a block diagram expressing the concept of the present invention, 
     FIG. 2 is a flow chart for representation of rational expression according to the present invention, 
     FIG. 3 is a flow chart showing calculation for obtaining the minimum polynomial, 
     FIG. 4 is a flow chart showing calculation for obtaining numerators of the representation of rational expression, 
     FIG. 5 is a block diagram for a processor in case where the representation of rational expression is impossible, 
     FIG. 6 is a flow chart showing the process in case where the representation of rational expression is impossible, 
     FIG. 7 is a view (1) showing positions of arms of a robot, and 
     FIG. 8 is a view (2) showing positions of the arms of the robot. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, preferred embodiments of the present invention will be described with reference to attached drawings. 
     As a program concerned in the present invention runs, a central processing unit (a digital processor) processes according to a concept of a device comprising the following means. 
     That is, as shown in FIG. 1, in a model in which restrictions among parameters are given by simultaneous algebraic equations with integral coefficients, when the simultaneous equations have only a finite number of solutions, the device represents zero points of a polynomial set F with integral coefficients, which represents the simultaneous equations and is described in a memory, by rational expressions based on zero points of a one-variable polynomial regarding one variable so that the device processes information using the representation of rational expression, wherein the device is an information processor comprising: 
     1. term order choosing means 21 for choosing an order O 1  among terms for facilitating the calculation of the Grobner basis, 
     2. Grobner basis calculating means 22 for calculating the Grobner basis G 1  of F with regard to O 1 , 
     3. minimum polynomial calculating means 23 for calculating the minimum polynomial f 1  based on G 1 , the minimum polynomial f 1  being a polynomial having the minimum degree of the variable X 1 , 
     4. decision means 24 for deciding whether the degree of f 1  (x 1 ) is equal to the number of solutions given from G 1  or not, and 
     5. polynomial representing means 25 for controlling the digital processor to obtain solutions represented by rational expressions {f l  (x 1 )=O, x 2  =f 2  (x 1 )/f&#39; 1  (x 1 ), . . . , x n  =f n  (x 1 )/f&#39; 1  (x 1 )} [notes: f&#39; 1  (x 1 ) is differential of f 1  (x 1 ).] when it is decided that the degree of f 1  (x 1 ) is equal to the number of the solutions given from G 1 . 
     The information processor executes the following algorithm for the calculating of the minimum polynomial and the representation of the solutions by rational expressions. 
     Algorithm--representation of rational expression (FIG. 4) 
     Input: polynomial set F in which the number of zero points is finite, term order O 1 , and variables x 1 , . . . , x n   
     Output: representation of zero points of F by rational expressions in case where the representation of solutions by rational expressions is possible 
     Step 21: G←Grobner basis of F with regard to O 1 , 
     Step 22: N←the number of zero points given by G 1 , 
     Step 23: f 1  ←the minimum polynomial of x 1  given by G 1 , 
     Step 24: decide whether deg (f 1 ) is equal to N or not, 
     Step 25: when deg (f 1 ) is not equal to N, shift to the calculation of Grobner basis (described later), and 
     Step 26: when deg (f 1 ) is equal to N, calculate the representation of rational expression and return the result. 
     Algorithm--calculation of the minimum polynomial (FIG. 2) 
     Input: term order O 1 , and variables x 1 , . . . , x n  of Grobner basis with regard to O 1   
     Output: the minimum polynomial of x 1   
     Step 31: (1) p←a prime number which does not divide any head coefficient of all elements of G 1  and is not used, 
     Step 32: f 1  (x 1 )←the minimum polynomial of x 1  regarding p as the modulus, 
     Step 33: E←a linear equation in which the coefficients of f 1  (x 1 ) are replaced by undetermined coefficients to calculate a normal form given by G 1  and the coefficients are eliminated and replaced by O, 
     Step 34: decide whether E has any solution or not, 
     Step 35: when E has no solution, return to (1), and 
     Step 36: when E has any solution, form the minimum polynomial based on the solution of E and then return it. 
     Algorithm--calculation of numerators of the representation of rational expression (FIG. 3) 
     Input: term order O 1 , variables x 1 , . . . , x n  of Grobner basis with regard to O 1 , the minimum polynomial f 1  (x 1 ) of x 1   
     Output: representation of rational expression 
     Step 41: (1) p←a prime number which does not divide any coefficient of the head terms of all elements of G 1  and is not used, 
     Step 42: G 2  ←Grobner basis with regard to the lexicographical order of φp (G 1 ), 
     Step 43: repeat the following steps 44 through 48 for every i (i=2, . . . , n), 
     Step 44: E←a linear equation in which the coefficients of f&#39; 1  (x 1 ) are replaced by undetermined coefficients in a normal form given by GI of f&#39; 1  (x 1 ) x i  and the coefficients are eliminated and replaced by O, 
     Step 45: decide whether E has any solution or not, 
     Step 46: when E has no solution, return to (1), 
     Step 47: when E has any solution, form gi based on the solution of E, 
     Step 48: return the representation of rational expression: 
     {f 1  (x 1 )0, x 2  =f 2  (x 1 )/f&#39; 1  (x 1 ), . . . , x n  =f n  (X 3 )/f&#39; 1  (x 1 )}. 
     In the present invention, first of all, the minimum polynomial of one variable is calculated. The degree of the polynomial is compared with the number of the solutions given by the inputted Grobner basis so as to determine whether the solutions can be represented by rational expressions with regard to the variable or not. When it is decided that the representation of rational expression is possible, the Grobner basis calculation on the rational number is executed and the representation of rational expression on the rational number is then given by the undetermined coefficient method and the linear equation. 
     To execute the undetermined coefficient method, it is necessary to obtain normal forms of some monomials. However, the number of the normal forms is equal to the number of the solutions at the most. 
     In the present invention, calculating linear equations is the most time-consuming stage, but the linear equations can be efficiently solved by first working out equations on the rational number and improving the accuracy by Hensel system. 
     Furthermore, the linear equations are solved by different digital processors, respectively, so that it only takes the real time required for solving a linear equation. 
     The followings are samples of simultaneous algebraic equations in which the number of solutions is finite. 
     K 5  =[u 0  +2u 1  +2u 2  +2u 3  +2u 4  +2u 5  -1, 
      2u 4  u 0  +(2u 3  +2u 5 ) u 1  +u 2   2  -u 4 , 
      2u 3  u 0  +(2u 2  +2u 4 ) u 1  +2u 5  u 2  -u 3 , 
      2u 2  u 0  +u 1   2  +2u 3  u 1  +(2u 4  -1) u 2  +2u 5  u 3 , 
      2u 1  u 0  +(2u 2  -1) u 1  +2u 3  u 2  +2u 4  u 3  +2u 5  u 4 , 
      u 0   2  -u 0  +2u 1   2  +2u 2   2  +2u 3   2  +2u 4   2  +2u 5   2  ] 
     K 6  =[u 0  +2u 1  +2u 2  +2u 3  +2u 4  +2u 5  +2u 6  -1, 
      2u 5  u 0  +(2u 4  +2u 6 ) u 1  +2u 3  u 2  -u 5 , 
      2u 4  u 0  +(2u 3  +2u 5 ) u 1  +u 2   2  +2u 6  u 2  -u 4 , 
      2u 3  u 0  +(2u 2  +2u 4 ) u 1  +2u 5  u 2  +(2u 6  -1) u 3 , 
      2u 2  u 0  +u 1   2  +2u 3  u 1  +(2u 4  -1) u 2  +2u 5  u 3  +2u 6  u 4 , 
      2u 1  u 0  +(2u 2  -1) u 1  +2u 3  u 2  +2u 4  u 3  +2u 5  u 4  +2u 6  u 5 , 
      u 0   2  -u 0  +2u 1   2  +2u 2   2  +2u 3   2  +2u 4   2  +2u 5   2  +2u 6   2  ] 
     K 7  =[u 0  +2u 1  +2u 2  +2u 3  +2u 4  +2u 5  +2u 6  +2u 7  -1, 
      2u 6  u 0  +(2u 5  +2u 7 ) u 1  +2u 4  u 2  +u 3   2  -u 6 , 
      2u 5  u 0  +(2u 4  +2u 6 ) u 1  +(2u 3  +2u 7 )u 2  -u 5 , 
      2u 4  u 0  +(2u 3  +2u 5 ) u 1  +u 2   2  +2u 6  u 2  +2u 7  u 3  -u 4 , 
      2u 3  u 0  +(2u 2  +2u 4 ) u 1  +2u 5  u 2  +(2u 6  -1) u 3  +2u 7  u 4 , 
      2u 2  u 0  +u 1   2  +2u 3  u 1  +(2u 4  -1) u 2  +2u 5  u 3  +2u 6  u 4  +2u 7  u 5 , 
      2u 1  u 0  +(2u 2  -1) u 1  +2u 3  u 2  +2u 4  u 3  +2u 5  u 4  +2u 6  u 5  +2u 7  u 6 , 
      u 0   2  -u 0  +2u 1   2  +2u 2   2  +2u 3   2  +2u 4   2  +2u 5   2  +2u 6   2  +2u 7   2  ] 
     In the above equations, as for K n  (n=5, 6, 7), the representation of solutions by rational expressions is possible with regard to x n . 
     C 6  =[abcde-1, 
      abcde+Bcdef+cdefa+defab+efabc+fabcd, 
      abcd+bcde+cdef+defa+efab+fabc, 
      abc+bcd+cde+def+efa+fab, 
      ab+bc+cd+de+ef+fa, 
      a+b+c+d+e+f] 
     Mod=[a+b+c+d+e, 
     (b+e) a+cb+dc+ed, 
     ((c+e) b+ed) a+dcb+edc, 
     ((ec+ed) b+edc) a+(e+1) dcb, 
     edcba-1] 
     As for K n , the minimum polynomial and the representation of rational expression with regard to X n  are found. 
     As for C 6 , the minimum polynomial and the representation of rational expression with regard to C 0  -C 1  +2C 2  -3C 3  -4C 4  +3C 5  are found. 
     As for Mod, the minimum polynomial and the representation of rational expression with regard to a-b+2c+d-e are found. 
     As for C 6  and Mod, the representation of rational expression is impossible with regard to any variables. Therefore, a search is conducted on the rational number on the system to obtain variables which allow the representation of solutions by rational expressions. 
     Table 1 shows the results in comparison of calculating speeds for the each problem by the conventional methods and the methods of the present invention. The calculating speeds are indicated in seconds required for calculating the representation of solutions by rational expressions after inputting the Grobner basis in the all degree inverse lexicographical order. The computer used for the calculations is FUJITSU S-4/61 (CPU: SuperSparc/60 MHz; Main storage 160 MB). 
     
                       TABLE 1                                                     
______________________________________                                    
          C.sub.6                                                         
                 Mod    K.sub.5 K.sub.6                                   
                                     K.sub.7                              
______________________________________                                    
GSL.sub.-Hensel                                                           
             32      41     11    141  1954                               
GSL-PoSSo   349      43      9    106  2140                               
GSL.sub.-Hensel-Para                                                      
             17      21      6     57   773                               
Dimenssion  156      64     32     64   128                               
______________________________________                                    
 
    
     In Table 1, the computing speeds (sec.) are measured when the problems are calculated by using PoSSo Library and the expression processing system Risa/Asir being developed by the inventor, running on FUJITSU S--4/61 (Super CPU, 60 MHz). 
     While the conventional method using a table of normal forms and symmetric expressions is executed in the PoSSo Library, the method of the present invention is executed in the Risa/Asir. 
     As for K 5  and K 6 , at first glance the PoSSo Library is better than the Risa/Asir. However, the greater the number of solutions, the smaller the difference therebetween and, as for K 7 , the Risa/Asir is better than the PoSSo Library. This is because with increasing the number of solutions, the time and memory required for calculating normal forms are rapidly increased in the conventional method. 
     As for C 6  and Mod, the Risa/Asir is better than the PoSSo Library wherein the difference is pronounced particularly in C 6 . This is because the number of solutions is greater and the number of resultant coefficients is smaller in C 6 . The method according to the present invention exhibits the pronounced effect on such a problem. Table 1 also shows the real times required for solving the linear equations in case of using the digital processor. Since the method of the present invention allows the most time-consuming parts to be processed in parallel, the great effect is apparently shown as compared with the conventional method. 
     &lt;When Representation of Rational Expressions is Impossible&gt; 
     When deg (f1)=N does not hold, it is decided that the calculation was failed. In this case, the process proceeds the following steps. The processing steps have been disclosed in Japanese Patent Application No. HO7-29154. 
     The processing steps are based on the following theorem. Hereinafter, the ideal elements generated by the polynomial set F will be referred as Id (F). 
     Theorem 
     When assuming F is an integral coefficient polynomial set, O 1  and O 2  are term orders, G 1  is Grobner basis of F with regard to O 1 , and p is a prime number, 
     Condition 1: if the head term of g with regard to O 1  is divisible by p for each element g of G 1  and φp (g) belongs to Id (F) (it should be noted that (p means the operation of selecting a prime number p which is impossible to divide any head coefficient of all elements of G 1  and replacing the coefficient by the remainder regarding the prime number p.), 
     i) φp (G,) is Grobner basis of φp (F) with regard to O 2 , and; 
     Condition 2: if there is an integral coefficient polynomial f h  belonging to Id (F) for each element h of G&#39; 2  and the head term of f h  with regard to O 2  is not divisible by p wherein the head terms of f h  and h with regard to O 2  coincide with each other when G&#39; 2  is the Grobner basis of φp (F) with regard to O 2 , 
     ii) G 2  {f h  .linevert split.h ((G)&#39; 2  } is Grobner basis of F with regard to O 2  &#39;. 
     In this theorem, the condition 2 is satisfied when the generation of the Grobner basis candidate by trace-lifting is successful. In the trace-lifting, after that, it is necessary to check whether G 2  is actually the Grobner basis or not. This is the most serious trouble in the above paragraph. However, according to this theorem, it can be found that G 2  is the Grobner basis without checking when the Grobner basis is already calculated in the other term order and the prime number p is selected in such a manner as to satisfy the condition 1. 
     Therefore, when the time required for calculating the Grobner basis in the other term order is smaller than the time required for the checking, the most serious trouble in the above paragraph can be avoided. 
     In this theorem, the condition 2 is satisfied when the generation of the Grobner basis candidate by trace-lifting is successful. In the trace-lifting, after that, it is necessary to check whether G 2  is actually the Grobner basis or not. This is the most serious trouble in the above paragraph. However, according to this theorem, it can be found that G 2  is the Grobner basis without checking when the Grobner basis is already calculated in the other term order and the prime number p is selected in such a manner as to satisfy the condition 1. 
     That is, the computer according to this embodiment has the following means as shown in FIG. 5: 
     (1) input means 1 for inputting a polynomial set F and term orders O 1  and O 2  ; 
     (2) prime number selecting means 2 for setting a prime number p which does not divide the coefficients of the head terms of all elements of F and is not used; 
     (3) G 1  calculating means 3 for calculating candidates (F, p, O 1 ) to obtain G 1  ; 
     (4) first decision means 4 for deciding whether G 1  is Grobner basis of Id (F) or not; 
     (5) first command means 5 for commanding the prime number selecting means 2 to reset the prime number p when the first decision means 4 decide that G 1  is not the Grobner basis; 
     (6) G 2  calculating means 6 for calculating candidates (G 1 , p, O 2 ) to obtain G 2  when the first decision means 4 decides that the G 1  is the Grobner basis, 
     (7) second decision means 7 for deciding whether G 2  is a polynomial set or not; 
     (8) output means 8 for outputting G 2  as the Grobner basis G of F with respect to O 2  when the second decision means 7 decides that G 2  is the polynomial set; and 
     (9) second command means 9 for commanding to retry the calculation from the start when the second decision means 7 decide that G 2  is not the polynomial set. 
     It should be noted that the device used for the representation of rational expression may be also used for the above means (1) through (3). 
     The generation of Grobner basis according to the flow chart shown in FIG. 6 is executed by the aforementioned means. 
     First of all, a polynomial set F and term order O 1  and O 2  are inputted by the inputting means 1, for example, a key board (Step 101). 
     Then, a prime number p, which does not divide any coefficient of the head terms of all elements of F and is not used, is set by the prime number means 2 (Step 102). By referring to coefficients of the head terms of F according to a subroutine not shown, the prime number p can be automatically set. 
     Candidates (F, p, O 1 ) are calculated by the G 1  calculating means 3 to obtain the Grobner basis G 1  of F with regard to O 1  (Step 103). 
     The first decision means 4 decides whether G 1  calculated by the G 1  calculating means 3 is Grobner basis of Id (F) or not (Step 104). That is, the first decision means 4 decides whether the head term of g with regard to O 1  is divisible by p for each element g of G 1  or not and whether φp (g) belongs to Id (F) or not. It is decided that φp (G 1 ) is the Grobner basis of φp (F) with regard to O 2 , when it is decided that the head term of g with regard to O 1  is divisible by p for each element g of G 1  and φp (g) belongs to Id (F) φp means the operation of selecting a prime number p which is impossible to divide any head coefficient of all elements of G 1  and replacing the coefficient by the remainder regarding the prime number p.) 
     When the first decision means 4 decide that G 1  is not the Grobner basis, the first command means 5 command the prime number selecting means 2 to reset the prime number p (Step 105). 
     When the first decision means 4 decides that the G, is the Grobner basis, the G 2  calculating means 6 calculates candidates (G 1 , p, O 2 ) to obtain G 2  (Step 106). 
     The second decision means 7 decide whether G 2  is a polynomial set or not (Step 107). That is, the second decision means 7 decide whether there is an integral coefficient polynomial f h  belonging to Id (F) for each element h of G&#39; 2  and the head term of f h  with regard to O 2  is not divisible by p or not and whether the head terms of f h  and h with regard to O 2  coincide with each other or not when G&#39; 2  is the Grobner basis of φp (F) with regard to O 2 . When it is decided that there is an integral coefficient polynomial f h  belonging to Id (F) for each element h of G&#39; 2  and the head term of f h  with regard to O 2  is not divisible by p and that the head terms of f h  and h with regard to O 2  coincide with each other when G&#39; 2  is the Grobner basis of φp (F) with regard to O 2 , the second decision means 7 decide that G 2  ={f h  .linevert split.h ((G)&#39; 2  } is Grobner basis of F with regard to O 2 . 
     When the second decision means 7 decide that G 2  is the polynomial set, the output means 8 outputs G 2  as the Grobner basis G of F with respect to O 2  when the second decision means 7 decide that G 2  is the polynomial set. 
     When the second decision means 7 decide that G 2  is not the polynomial set, the second command means command to retry the calculation from the start. 
     According to the above process, the best Grobner basis can be obtained even when the representation of rational expression is impossible, thereby optimizing the information processing. 
     &lt;Applications of the Present Invention&gt; 
     The present invention can be applied to such fields as follows. 
     Application 1: problems relating to the movement of a robot 
     Imagine, a state where one object (rigid body) 50 is supported by six arms 51 through 56 standing on a ground Grobner which are variable in length as shown in FIGS. 7 and 8. 
     At this point, problems of calculating the position of the object based on the length of the arms and the positions of arms relative to the object and the ground are immediately converted to nonlinear simultaneous equations. 
     In the robot technology, huge studies have been conducted on the relation between the way of mounting the arms and the number of the possible positions. Such studies need to obtain values such as the number of &#34;real solutions&#34; of the given equation, which are not obtained by the conventional numerical methods. The method of the present invention is effective for such a case. 
     Application 2: condition (phase) analysis of magnetic substances 
     The description will be made as regard to K 5 , K 6 , and K 7  discussed above. Besides ferromagnetism and paramagnetism, there is Spin-glass as one of phases of magnetic substances. An integral equation is obtained by considering a Beth gridded random Ising model as one of models statistically working on the phase. A series of algebraic equations are obtained when finding non-continuous solutions at the absolute zero point of the integral equation. The series of algebraic equations are the non-linear simultaneous algebraic equation of variable n+1 described as kn. 
     The equation is solved for n=5, 6, 7, . . . with high precision by the present invention, thereby expecting a case where n becomes infinity and thus obtaining the solutions based on the expectation. 
     Other Applications: 
     Besides the above application, the inverse kinnematical calculation for finding the rotational angle of each Joint based on coordinates of the top of a normal articulated robot is well known in the robot technology. In Runge-Kutta method as one of effective methods for numerically solving differential equations, it is necessary to solve non-linear simultaneous algebraic equations for obtaining the best values of appeared parameters. The present invention is applicable to various information processing and controlling units requiring such calculation. 
     The present invention reduces the number of times required for calculating normal forms to calculate the minimum polynomial. Therefore, it can be decided in a short time whether the representation of rational expression is possible or not, whereby the linear equations are solved in such a time as corresponding the volume of the result. In addition, the molecules of the rational expressions can be obtained independently from each other and are solved in a parallel computer or in the distributed calculating environment, thereby making the calculating speed higher in the real time.