Let a be a permutation of the vertex set V(G) of a connected graph G. Define the total relative displacement of alpha in G by [GRAPHIC] where d(G) (x, y) is the length of the shortest path between x and y in G. Let pi...
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Let a be a permutation of the vertex set V(G) of a connected graph G. Define the total relative displacement of alpha in G by [GRAPHIC] where d(G) (x, y) is the length of the shortest path between x and y in G. Let pi*(G) be the maximum value of delta (alpha)(G) among all permutations of V(G). The permutation which realizes pi*(G) is called a chaotic mapping of G. In this paper, we study the chaotic mappings of complete multipartite graphs. The problem is reduced to a quadratic integer programming problem. We characterize its optimal solution and present an algorithm running in O(n(5) log n) time, where n is the total number of vertices in a complete multipartite graph.
Solving convex quadraticinteger minimization problems by a branch-and-bound algorithm requires tight lower bounds on the optimal objective value. To obtain such dual bounds, we follow the approach of [C. Buchheim, A....
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Solving convex quadraticinteger minimization problems by a branch-and-bound algorithm requires tight lower bounds on the optimal objective value. To obtain such dual bounds, we follow the approach of [C. Buchheim, A. Caprara, and A. Lodi, Math. Program., 135 (2012), pp. 369-395] and underestimate the objective function by another convex quadratic function that can be minimized over the integers by simply rounding its continuous minimizer. In geometric terms, we approximate the sublevel sets of the original objective function by auxiliary ellipsoids having the strong rounding property, introduced by [R. Hubner and A. Schobel, European J. Oper. Res., 237 (2014), pp. 404-410]. We first consider axisparallel ellipsoids (corresponding to separable convex quadratic functions) and show how to efficiently compute an axisparallel ellipsoid yielding the tightest lower bound, both in the situation where the location of the continuous minimizer is given and in the situation where it varies, as it happens in a branch-and-bound approach. In the latter case, we compute both worst-case and average-case optimal ellipsoids. Moreover, we consider the class of quasi-round ellipsoids (from Hubner and Schobel). In this case, we do not know whether optimal auxiliary ellipsoids can be computed efficiently. However, we present a heuristic for computing an appropriate quasi-round ellipsoid that still yields valid dual bounds;it turns out that using this approach within a branch-and-bound scheme outperforms the approaches based on axisparallel ellipsoid in terms of running times. We finally combine both approaches by introducing the concept of quasi-axisparallel ellipsoids and present a corresponding extension of the heuristic bound computation.
Consider the semidefinite relaxation (SDR) of the quadraticinteger program (QIP): gamma := max {x(T) Qx : x is an element of {-1, 1}(n)} . Thus we show that 'breaching' the SDR gap for the QIP problem is as d...
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Consider the semidefinite relaxation (SDR) of the quadraticinteger program (QIP): gamma := max {x(T) Qx : x is an element of {-1, 1}(n)} <= min {trace(D) : D - Q greater than or similar to 0} =: (gamma) over bar where Q is a given symmetric matrix and D is diagonal. We consider the SDR gap (gamma) over bar gamma. We establish the uniqueness of the SDR solution and prove that gamma = (gamma) over bar if and only if gamma(r) := n(-1) max {x(T) VVT x : x is an element of {-1, 1}(n)} = 1 where V is an orthogonal matrix whose columns span the (r - dimensional) null space of D - Q and where D is the unique SDR solution. We also give a test for establishing whether gamma = (gamma) over bar that involves 2(r-1) function evaluations. In the case that gamma(r) < 1 we derive an upper bound on gamma which is tighter than <(gamma)over bar>. Thus we show that 'breaching' the SDR gap for the QIP problem is as difficult as the solution of a QIP with the rank of the cost function matrix equal to the dimension of the null space of D - Q. This reduced rank QIP problem has been recently shown to be solvable in polynomial time for fixed r.
quadratic integer programming problems with cardinality constraint have many applications in real life. Portfolio selection is an important application in financial optimization. In this paper we develop an exact and ...
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quadratic integer programming problems with cardinality constraint have many applications in real life. Portfolio selection is an important application in financial optimization. In this paper we develop an exact and efficient algorithm for quadratic integer programming problems with cardinality constraint. This iterative algorithm is actually a branch and bound method, which adopts a domain cut and partition scheme. Removing cardinality constraint and integrality constraints on variables, the relaxation problem is a quadraticprogramming problem. By solving the quadraticprogramming problem, we find a lower bound for the optimal objective function value of the primal problem. The domain cut technique is used to cut off some regions that do not contain any feasible solution better than the incumbent solution. Thus the optimality gap is reduced greatly. The finite number of iterations is clear from the fact that there are only a finite number of feasible integer solutions in the feasible region. Encouraging computational results are also reported in the paper.
We consider the problem of minimizing a general quadratic function over a polytope in the n-dimensional space with integrality restrictions on all of the variables. (This class of problems contains, e.g., the quadrati...
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We consider the problem of minimizing a general quadratic function over a polytope in the n-dimensional space with integrality restrictions on all of the variables. (This class of problems contains, e.g., the quadratic 0-1 program as a special case.) A finite branch and bound algorithm is established, in which the branching procedure is the so-called "integral rectangular partition", and the bound estimation is performed by solving a concave programming problem with a special structure. Three methods for solving this special concave program are proposed.
We consider the maximization T gamma = max{x(T)Ax : x. {- 1, 1}(n)} for a given symmetric A epsilon R-n x n. It was shown recently, using properties of zonotopes and hyperplane arrangements, that in the special case t...
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We consider the maximization T gamma = max{x(T)Ax : x. {- 1, 1}(n)} for a given symmetric A epsilon R-n x n. It was shown recently, using properties of zonotopes and hyperplane arrangements, that in the special case that A has a small rank, so that A = VVT where V epsilon R-nxm with m < n, then there exists a polynomial time algorithm ( polynomial in n for a given m) to solve the problem max{x(T)VV(T) x : x epsilon {-1,1}(n)}. In this paper, we use this result, as well as a spectral decomposition of A to obtain a sequence of non-increasing upper bounds on gamma with no constraints on the rank of A. We also give easily computable necessary and sufficient conditions for the absence of a gap between the solution and its upper bound. Finally, we incorporate the semidefinite relaxation upper bound into our scheme and give an illustrative example.
It is shown how to replace the objective function of an integerquadraticprogramming problem by an integer objective function whose size is polynomially bounded by the number of variables and the size of the constrai...
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It is shown how to replace the objective function of an integerquadraticprogramming problem by an integer objective function whose size is polynomially bounded by the number of variables and the size of the constraints, without changing the set of optimal solutions. The Frank and Tardos' algorithm [1] is used which in turn uses the simultaneous approximation algorithm of Lenstra et al. [4]. This preprocessing algorithm assures that the running time of any algorithm for solving integerquadraticprogramming problems can be made independent of the size of the objective function coefficients.
Ellipsoid bounds for strictly convex quadraticinteger programs have been proposed in the literature. The idea is to underestimate the strictly convex quadratic objective function q of the problem by another convex qu...
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Ellipsoid bounds for strictly convex quadraticinteger programs have been proposed in the literature. The idea is to underestimate the strictly convex quadratic objective function q of the problem by another convex quadratic function with the same continuous minimizer as q and for which an integer minimizer can be easily computed. We initially propose in this paper a different way of constructing the quadratic underestimator for the same problem and then extend the idea to other quadraticinteger problems, where the objective function is convex (not strictly convex), and where the objective function is nonconvex and box constraints are introduced. The quality of the bounds proposed is evaluated experimentally and compared to the related existing methodologies.
We present in this paper an integer diagonalization approach for deriving new lower bounds for general quadratic integer programming problems. More specifically, we introduce a semiunimodular transformation in order t...
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We present in this paper an integer diagonalization approach for deriving new lower bounds for general quadratic integer programming problems. More specifically, we introduce a semiunimodular transformation in order to diagonalize a symmetric matrix and preserve integral property of the feasible set at the same time. Via the semiunimodular transformation, the resulting separable quadraticinteger program is a relaxation of the nonseparable quadraticinteger program. We further define the integer diagonalization dual problem to identify the best semiunimodular transformation and analyze some basic properties of the set of semiunimodular transformations for a rational symmetric matrix. In particular, we present a complete characterization of the set of all semiunimodular transformations for a nonsingular 2x2 symmetric matrix. We finally discuss Lagrangian relaxation and convex relaxation schemes for the resulting separable quadratic integer programming problem and compare the tightness of different relaxation schemes.
We present an implicit enumeration algorithm for a nonseparable quadratic integer programming problem. We utilize fathoming criteria derived from Lemke's complementary pivot algorithm, and compare the use of pseud...
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We present an implicit enumeration algorithm for a nonseparable quadratic integer programming problem. We utilize fathoming criteria derived from Lemke's complementary pivot algorithm, and compare the use of pseudo-costs versus generalized penalties as a guide to branching. Computational experience is provided.
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