ccehc an efficient local search algorithm for weighted partial maximum satisfiability weighted maximum satisfiability and unweighted partial maximum satisfiability pms are two significant generalizations of maximum satisfiability max sat and weighted partial maximum satisfiability wpms is the combination of the two with more important applications in practice recently great breakthroughs have been made on stochastic local search sls for weighted max sat and pms resulting in several state of the art sls algorithms ccls dist and distup however compared to the great progress of sls on weighted max sat and pms the performance of sls on wpms lags far behind in this paper we present a new sls algorithm named ccehc for wpms ccehc employs an extended framework of ccls with a heuristic emphasizing hard clauses called ehc with strong accents on hard clauses ehc has three components a variable selection mechanism focusing on configuration checking based only on hard clauses a weighting scheme for hard clauses and a biased random walk component extensive experiments demonstrate that ccehc significantly outperforms its state of the art sls competitors further experimental results on comparing ccehc with a state of the art complete solver show the effectiveness of ccehc on a number of application wpms instances and indicate that ccehc might be beneficial in practice also empirical analyses confirm the effectiveness of each component underlying the ehc heuristic

a heuristic method for the set covering problem we present a lagrangian based heuristic for the well known set covering problem scp the algorithm was initially designed for solving very large scale scp instances involving up to 5 000 rows an

affine collineations in space time the existence of affine collineations in space time is discussed and the types of space time admitting proper affine collineations is displayed the close connection between such space times and their holonomy structure and local decomposability is established affine collineations with fixed points are also considered as is the problem of extending local affine collineations to the whole of space time

covariantly constant tensors and holonomy structure in general relativity this paper attempts to give a comprehensive discussion of space times that admit vector fields or second order symmetric or skew symmetric tensor fields which are covariantly constant or recurrent the relationship between such space times m and their holonomy group is given

special conformal killing vector space times and symmetry inheritance viscous heat conducting fluid and anisotropic fluid space times admitting a special conformal killing vector sckv are studied and some general theorems concerning the inheritance of the symmetry associated with the sckv are proved in particular for viscous fluid space times it is shown that i if the sckv maps fluid flow lines into fluid flow lines then all physical components of the energy momentum tensor inherit the sckv symmetry or ii if the lie derivative along a sckv of the shear viscosity term ab is zero then again we have symmetry inheritance all space times admitting a sckv and satisfying the dominant energy condition are found apart from the vacuum pp wave solutions which are the only vacuum solutions that can admit a sckv the energy momentum tensor associated with these space times is shown to admit at least one null eigenvector and can represent either a viscous fluid with heat conduction or an anisotropic fluid no perfect fluid space times can admit a sckv these sckv space t

ricci collineation vectors in fluid space times the properties of fluid space times that admit a ricci collineation vector rcv parallel to the fluid unit four velocity vector ua are briefly reviewed these properties are expressed in terms of the kinematic quantities of the timelike congruence generated by ua the cubic equation derived by oliver and davis ann inst henri poincare 30 339 1979 for the equation of state p p of a perfect fluid space time that admits an rcv which does not degenerate to a killing vector is solved for physically realistic fluids necessary and sufficient conditions for a fluid space time to admit a spacelike rcv parallel to a unit vector na orthogonal to ua are derived in terms of the expansion shear and rotation of the spacelike congruence generated by na perfect fluid space times are studied in detail and analogues of the results for timelike rcvs parallel to ua are obtained properties of imperfect fluid space times for which the energy flux vector qa vanishes and na is a spacelike eigenvector of the aniso

a genetic algorithm for the set covering problem abstract in this paper we present a genetic algorithm based heuristic for non unicost set covering problems we propose several modifications to the basic genetic procedures including a new fitness based crossover operator fusion a variable mutation rate and a heuristic feasibility operator tailored specifically for the set covering problem the performance of our algorithm was evaluated on a large set of randomly generated problems computational results showed that the genetic algorithm based heuristic is capable of producing high quality solutions

can adaption help on the average we study adaptive information for approximation of linear problems in a separable hilbert space equipped with a probability measure it is known that adaption does not help in the worst case for linear problems we prove that adaption also doesnot help on the average that is there exists nonadaptive information which is as powerful as adaptive information this result holds for orthogonally invariant measures we provide necessary and sufficient conditions for a measure to be orthogonally invariant examples of orthogonally invariant measures include gaussian measures and in the finite dimensional case weighted lebesgue measures

incorporation of space time symmetries in einstein s field equations in the search for exact solutions to einstein s field equations the main simplification tool is the introduction of space time symmetries motivated by this fact we develop a method to write the field equations for general matter in a form that fully incorporates the character of the symmetry the method is being expressed in a covariant formalism using the framework of a double congruence the basic notion on which it is based is that of the geometrization of a general symmetry as a special application of our general method we consider the case of a space like conformal killing vector field on the space time manifold regarding special types of matter fields new perspectives in general relativity are discussed

statistical estimation and optimal recovery new formulas are given for the minimax linear risk in estimating a linear functional of an unknown object from indirect data contaminated with random gaussian noise the formulas cover a variety of loss functions and do not require the symmetry of the convex a priori class it is shown that affine minimax rules are within a few percent of minimax even among nonlinear rules for a variety of loss functions it is also shown that difficulty of estimation is measured by the modulus of continuity of the functional to be estimated the method of proof exposes a correspondence between minimax affine estimates in the statistical estimation problem and optimal algorithms in the theory of optimal recovery

ricci and contracted ricci collineations of the robertson walker space time ricci collineations and contracted ricci collineations of the robertson walker metric associated with a vector field of the form 0 t r 1 t r 0 0 are presented

circle detection using electro magnetism optimization nature inspired computing has yielded remarkable applications of collective intelligence which considers simple elements for solving complex tasks by common interaction on the other hand automatic circle detection in digital images has been considered an important and complex task for the computer vision community that has devoted a tremendous amount of research seeking for an optimal circle detector this paper presents an algorithm for the automatic detection of circular shapes embedded into cluttered and noisy images without considering conventional hough transform techniques the approach is based on a nature inspired technique known as the electro magnetism optimization emo it follows the electro magnetism principle regarding a collective attraction repulsion mechanism which manages particles towards an optimal solution each particle represents a solution by holding a charge which is related to the objective function to be optimized the algorithm uses the encoding of three non collinear points embedded into an edge only image as candidate circles guided by the values of the objective function the set of encoded candidate circles charged particles are evolved using an emo algorithm so that they can fit into actual circular shapes over the edge only map of the image experimental evidence from several tests on synthetic and natural images which provide a varying range of complexity validates the efficiency of our approach regarding accuracy speed and robustness

algorithms for railway crew management crew management is concerned with building the work schedules of crews needed to cover a planned timetable this is a well known problem in operations research and has been historically associated with airlines and mass transit companies more recently railway applications have also come on the scene especially in europe in practice the overall crew management problem is decomposed into two subproblems called crew scheduling and crew rostering in this paper we give an outline of different ways of modeling the two subproblems and possible solution methods two main solution approaches are illustrated for real world applications in particular we discuss in some detail the solution techniques currently adopted at the italian railway company ferrovie dello stato spa for solving crew scheduling and rostering problems

affine collineations in riemannian spaces sufficient conditions on the christoffel symbols and metric tensors to insure the existence of affine collineations in riemann spaces are obtained a proof of the group property of affine collineations is given several examples of physically relevant riemannian spaces admitting affine collineations are presented and the constants of motion are constructed

a systematic approach to self similarity in newtonian space time after an introductory mathematical review of the general concept of self similarity with respect to a given rescaling algebra attention is focused on the case of newtonian systems in galilean space time whose self similarity transformations will form subgroups of the maximal self similarity group of the galilean space time structure itself as a prerequisite for a systematic general investigation of self similarity in such newtonian systems it is shown how an appropriately adapted similarity transporting coordinate system can be constructed explicitly for an arbitrary generator of the 12 parameter galilean self similarity group a concrete application is provided by the case of the keplerian disk which is kinematically self similar under the action of a three parameter subgroup it is shown in the explicit example of a eulerian fluid system how the generic self similarity problem can be formulated as an effective stationarity problem

geometrization of a general collineation geometrization of a general collineation means to express the collineation as necessary and sufficient conditions on the kinematic quantities shear vorticity expansion of the congruence of the vector field generating the collineation it is shown that the generic form of a collineation is l gab 2 gab hab where hab is a traceless symmetric tensor a general theorem concerning the geometrization of the generic collineation is presented and its applications are discussed

a 3 flip neighborhood local search for the set covering problem the set covering problem scp calls for a minimum cost family of subsets from n given subsets which together covers the entire ground set in this paper we propose a local search algorithm for scp which has the following three characteristics 1 the use of 3 flip neighborhood which is the set of solutions obtainable from the current solution by exchanging at most three subsets as the size of 3 flip neighborhood is o n3 the neighborhood search becomes expensive if implemented naively to overcome this we propose an efficient implementation that reduces the number of candidates in the neighborhood without sacrificing the solution quality 2 we allow the search to visit the infeasible region and incorporate the strategic oscillation technique realized by adaptive control of penalty weights 3 the size reduction of the problem by using the information from the lagrangian relaxation is incorporated which is indispensable for solving very large instances according to computational comparisons on benchmark instances with other existing heuristic algorithms for scp our algorithm performs quite effectively for various types of problems especially for very large scale instances

an algorithm for set covering problem in this paper we present an algorithm for the set covering problem that combines problem reduction tests with dual ascent subgradient optimisation and linear programming computational results are presented for problems involving up to 400 rows and 4000 columns

curvature inheritance symmetry in riemannian spaces with applications to fluid space times katzin et al g h katzin j levine and w r davis j math phys 10 617 1969 introduced curvature collineations cc defined by a vector satisfying l rbcda 0 where rbcda is the riemann curvature tensor of a riemannian space vn and l denotes the lie derivative they proved that a cc is related to a special conformal motion which implies the existence of a covariant constant vector field unfortunately recent study indicates that the existence of a covariant constant vector restricts vn to a very rare special case with limited physical use in particular for a fluid space time with special conformal motion either stiff or unphysical equations of state are singled out moreover perfect fluid space times do not admit special conformal motions this information was not available in 1969 when cc symmetry was introduced in this paper cc is generalized to another symmetry called curvature inheritance ci satisfying l rbcda 2 rbcda where is a scalar function we prove that a proper

do linear problems have linear optimal algorithms a selective introduction to the field of information based complexity is presented in the context of the question raised in the title after introducing some of the basic ideas of this relatively new area that interfaces mathematics and theoretical computer science the article surveys results on the existence of linear optimal algorithms for linear problems several illustrative examples are given along with an indication of the variety of disciplines in which techniques of information based complexity are being applied known under aliases such as the general theory of optimal algorithms and the information centered approach to algorithms information based complexity seeks to create a general theory about problems with partial or approximate information and to apply the results to specific problems some of the disciplines where problems with such incomplete information have arisen include computer science economics control theory signal processing and geophysics the goal of this article is to present a selective introduction to the field of information based complexity and to describe the seesaw nature of results in the last decade on the extent to which linear problems have linear optimal algorithms the approach we take will certainly not do justice to the breadth of ideas techniques and applications that are coming into play in the general theory instead we will take a direct route to the results on linear optimal algorithms pausing occasionally to survey the pleasing way in which ideas from linear algebra and functional analysis are used in the final section we mention some other theoretical and applied topics currently under investigation in information based complexity a more general expository overview can be found in traub and wozniakowski 15 and more technical surveys appear in packel and wozniakowski 10 and wozniakowski 21 2 two preliminary examples we set the stage for an exposition of the general linear theory by imposing partial information on two problems which are known to virtually every student of mathematics the problem of integrating a continuous function needs no introduction the fourier series approach to approximating func tions by linear combinations of sines and cosines is almost as familiar we do not develop these ideas as a testimony to the power of the general theory more about that later but rather to have a comfortable base to refer to when the generalizations and abstractions are introduced integration example let f be a function from the space w 0 1 of real valued continuous functions on the interval 0 1 we would like to obtain a value for the

an electromagnetism metaheuristic for the unicost set covering problem in this paper we propose a new heuristic algorithm to solve the unicost version of the well known set covering problem the method is based on the electromagnetism metaheuristic approach which after generating a pool of solutions to create the initial population applies a fixed number of local search and movement iterations based on the electromagnetism theory in addition to some random aspects used in the construction and local search phases we also apply mutation in order to further escape from local optima the proposed algorithm has been tested over 80 instances of the literature on the classical benchmark instances where the number of columns is larger than the number of rows the algorithm by using a fixed set of parameters always found the best known solution and for 12 instances it was able to improve the current best solution by using different parameter settings the algorithm improved 4 additional best known solutions moreover we proved the effectiveness of the electromagnetism metaheuristic approach for the unicost set covering problem by embedding the procedures of the proposed algorithm in a genetic algorithm scheme the worse results obtained by the genetic algorithm show the impact of the electromagnetism metaheuristic approach in conducting the search of the solution space by applying the movements based on the electromagnetism theory finally we report the results obtained by modifying the proposed electromagnetism metaheuristic algorithm for solving the non unicost set covering problem

an efficient local search heuristic with row weighting for the unicost set covering problem abstract the set covering problem scp is np hard we propose a new row weighting local search rwls algorithm for solving the unicost variant of the scp i e uscps where the costs of all sets are identical rwls is a heuristic algorithm that has three major components united in its local search framework 1 a weighting scheme which updates the weights of uncovered elements to prevent convergence to local optima 2 tabu strategies to avoid possible cycles during the search and 3 a timestamp method to break ties when prioritizing sets rwls has been evaluated on a large number of problem instances from the or library and compared with other approaches it is able to find all the best known solutions bks and improve 14 of them although requiring a higher computational effort on several instances rwls is especially effective on the combinatorial or library instances and can improve the best known solution to the hardest instance cyc11 considerably rwls is conceptually simple and has no instance dependent parameters which makes it a practical and easy to use uscp solver

an effective and simple heuristic for the set covering problem abstract this paper investigates the development of an effective heuristic to solve the set covering problem scp by applying the meta heuristic meta raps meta heuristic for randomized priority search in meta raps a feasible solution is generated by introducing random factors into a construction method then the feasible solutions can be improved by an improvement heuristic in addition to applying the basic meta raps the heuristic developed herein integrates the elements of randomizing the selection of priority rules penalizing the worst columns when the searching space is highly condensed and defining the core problem to speedup the algorithm this heuristic has been tested on 80 scp instances from the or library the sizes of the problems are up to 1000 rows 10 000 columns for non unicost scp and 28 160 rows 11 264 columns for the unicost scp this heuristic is only one of two known scp heuristics to find all optimal best known solutions for those non unicost instances in addition this heuristic is the best for unicost problems among the heuristics in terms of solution quality furthermore evolving from a simple greedy heuristic it is simple and easy to code this heuristic enriches the options of practitioners in the optimization area

spacelike conformal killing vectors and spacelike congruences necessary and sufficient conditions are derived for space time to admit a spacelike conformal motion with symmetry vector parallel to a unit spacelike vector field na these conditions are expressed in terms of the shear and expansion of the spacelike congruence generated by na and in terms of the four velocity of the observer employed at any given point of the congruence it is shown that either the expansion or the rotation of this spacelike congruence must vanish if dna dp 0 where p denotes arc length measured along the integral curves of na and also that there exist no proper spacelike homothetic motions with constant expansion propagation equations for the projection tensor and the rotation tensor are derived and it is proved that every isometric spacelike congruence is rigid fluid space times are studied in detail a relation is established between spacelike conformal motions and material curves in the fluid if a fluid space time admits a spacelike conformal killing vector parallel to na and