The algorithm was not a computational break-through, as the simplex method is more efficient for all but specially constructed families of linear programs. However, Khachiyan's algorithm inspired new lines of research in linear programming.
In , N. Karmarkar proposed a projective method for linear programming. Karmarkar's algorithm improved on Khachiyan's worst-case polynomial bound giving O n 3. Karmarkar claimed that his algorithm was much faster in practical LP than the simplex method, a claim that created great interest in interior-point methods. Affine scaling is one of the oldest interior point methods to be developed. It was developed in the Soviet Union in the mids, but didn't receive much attention until the discovery of Karmarkar's algorithm, after which affine scaling was reinvented multiple times and presented as a simplified version of Karmarkar's.
Affine scaling amounts to doing gradient descent steps within the feasible region, while rescaling the problem to make sure the steps move toward the optimum faster. In , Vaidya developed an algorithm that runs in O n 2. For both theoretical and practical purposes, barrier function or path-following methods have been the most popular interior point methods since the s. The current opinion is that the efficiencies of good implementations of simplex-based methods and interior point methods are similar for routine applications of linear programming.
Covering and packing LPs can be solved approximately in nearly-linear time. There are several open problems in the theory of linear programming, the solution of which would represent fundamental breakthroughs in mathematics and potentially major advances in our ability to solve large-scale linear programs. This closely related set of problems has been cited by Stephen Smale as among the 18 greatest unsolved problems of the 21st century.
In Smale's words, the third version of the problem "is the main unsolved problem of linear programming theory. The development of such algorithms would be of great theoretical interest, and perhaps allow practical gains in solving large LPs as well.
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Although the Hirsch conjecture was recently disproved for higher dimensions, it still leaves the following questions open. These questions relate to the performance analysis and development of simplex-like methods. The immense efficiency of the simplex algorithm in practice despite its exponential-time theoretical performance hints that there may be variations of simplex that run in polynomial or even strongly polynomial time.
It would be of great practical and theoretical significance to know whether any such variants exist, particularly as an approach to deciding if LP can be solved in strongly polynomial time. The simplex algorithm and its variants fall in the family of edge-following algorithms, so named because they solve linear programming problems by moving from vertex to vertex along edges of a polytope. This means that their theoretical performance is limited by the maximum number of edges between any two vertices on the LP polytope. As a result, we are interested in knowing the maximum graph-theoretical diameter of polytopal graphs.
It has been proved that all polytopes have subexponential diameter. The recent disproof of the Hirsch conjecture is the first step to prove whether any polytope has superpolynomial diameter. If any such polytopes exist, then no edge-following variant can run in polynomial time. Questions about polytope diameter are of independent mathematical interest. Simplex pivot methods preserve primal or dual feasibility. On the other hand, criss-cross pivot methods do not preserve primal or dual feasibility—they may visit primal feasible, dual feasible or primal-and-dual infeasible bases in any order.
Pivot methods of this type have been studied since the s. In contrast to polytopal graphs, graphs of arrangement polytopes are known to have small diameter, allowing the possibility of strongly polynomial-time criss-cross pivot algorithm without resolving questions about the diameter of general polytopes. If all of the unknown variables are required to be integers, then the problem is called an integer programming IP or integer linear programming ILP problem. In contrast to linear programming, which can be solved efficiently in the worst case, integer programming problems are in many practical situations those with bounded variables NP-hard.
This problem is also classified as NP-hard, and in fact the decision version was one of Karp's 21 NP-complete problems. If only some of the unknown variables are required to be integers, then the problem is called a mixed integer programming MIP problem. There are however some important subclasses of IP and MIP problems that are efficiently solvable, most notably problems where the constraint matrix is totally unimodular and the right-hand sides of the constraints are integers or — more general — where the system has the total dual integrality TDI property.
Such integer-programming algorithms are discussed by Padberg and in Beasley. A linear program in real variables is said to be integral if it has at least one optimal solution which is integral. Integral linear programs are of central importance in the polyhedral aspect of combinatorial optimization since they provide an alternate characterization of a problem.
Conversely, if we can prove that a linear programming relaxation is integral, then it is the desired description of the convex hull of feasible integral solutions. Terminology is not consistent throughout the literature, so one should be careful to distinguish the following two concepts,.
One common way of proving that a polyhedron is integral is to show that it is totally unimodular. There are other general methods including the integer decomposition property and total dual integrality. A bounded integral polyhedron is sometimes called a convex lattice polytope , particularly in two dimensions. Permissive licenses:. MINTO Mixed Integer Optimizer, an integer programming solver which uses branch and bound algorithm has publicly available source code  but is not open source.
Proprietary licenses:. A reader may consider beginning with Nering and Tucker, with the first volume of Dantzig and Thapa, or with Williams. From Wikipedia, the free encyclopedia. Main article: Dual linear program. In a linear programming problem, a series of linear constraints produces a convex feasible region of possible values for those variables.
In the two-variable case this region is in the shape of a convex simple polygon. Main article: Karmarkar's algorithm. Main article: Affine scaling. Does linear programming admit a strongly polynomial-time algorithm? Convex programming Dynamic programming Expected shortfall Optimization of expected shortfall Input—output model Job shop scheduling Linear-fractional programming LFP LP-type problem Mathematical programming Nonlinear programming Oriented matroid Quadratic programming , a superset of linear programming Semidefinite programming Shadow price Simplex algorithm , used to solve LP problems.
CRC Press. Theory of Linear and Integer Programming. Dantzig April Operations Research Letters. George Bernard , Linear programming. Thapa, Mukund Narain.
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New York: Springer. Mathematical Programming, Series B.
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Mathematical Programming. The Mathematical Intelligencer. Speeding-up linear programming using fast matrix multiplication.
CN102662735B - 面向实时感知环境的复合事件检测方法及系统 - Google Patents
Efficient inverse maintenance and faster algorithms for linear programming. European Journal of Operational Research. Young Bibcode : arXiv Optimization : Algorithms , methods , and heuristics. Unconstrained nonlinear.