the traditional approach towards generating lift-and-project cuts involves solving a cut generating linear program (CGLP) that grows prohibitively large if a multiple-term disjunction is used instead of the classical ...
详细信息
the proceedings contain 32 papers. the special focus in this conference is on Edge Connectivity and Algorithms. the topics include: A characterization of weakly bipartite graphs;bipartite designs;characterizing nonint...
ISBN:
(纸本)354064590X
the proceedings contain 32 papers. the special focus in this conference is on Edge Connectivity and Algorithms. the topics include: A characterization of weakly bipartite graphs;bipartite designs;characterizing noninteger polyhedra with 0-1 constraints;a theorem of truemper;the generalized stable set problem for claw-free bidirected graphs;on a min-max theorem of cacti;edge-splitting and edge-connectivity augmentation in planar graphs;a new bound for the 2-edge connected subgraph problem;an approximation algorithm for 2-edge connected spanning subgraphs;multicuts in unweighted graphs with bounded degree and bounded tree-width;approximating disjoint-path problems using greedy algorithms and packing integer programs;approximation algorithms for the mixed postman problem;improved approximation algorithms for uncapacitated facility location;the maximum traveling salesman problem under polyhedral norms;polyhedral combinatorics of benzenoid problems;consecutive ones and a betweenness problem in computational biology;solving a linear diophantine equation with lower and upper bounds on the variables;the intersection of knapsack polyhedra and extensions;new classes of lower bounds for bin packing problems;solving integer and disjunctive programs by lift and project;a class of hard small 0-1 programs;building chain and cactus representations of all minimum cuts from hao-orlin in the same asymptotic run time;simple generalized maximum flow algorithms;the pseudoflow algorithm and the pseudoflow-based simplex for the maximum flow problem;an implementation of a combinatorial approximation algorithm for minimum-cost multicommodity flow and non-approximability results for scheduling problems with minsum criteria.
We start with definitions given by Plotkin, Shmoys, and Tardos [16]. Given A∈?m×n, b∈?m and a polytope P $
 \subseteq$
 \subseteq ? n , the fractional packing problem is to find an x ∈ P such t...
ISBN:
(纸本)3540660194
We start with definitions given by Plotkin, Shmoys, and Tardos [16]. Given A∈?m×n, b∈?m and a polytope P $
\subseteq$
\subseteq ? n , the fractional packing problem is to find an x ∈ P such that Ax ≤ b if such an x exists. An ∈-approximate solution to this problem is an x ∈ P such that Ax ≤ (1+∈)b. An ∈-relaxed decision procedure always finds an ∈-approximate solution if an exact solution exists.
We study the problem of optimizing over the set of all combinatorial embeddings of a given planar graph. Our objective function prefers certain cycles of G as face cycles in the embedding. the motivation for studying ...
详细信息
ISBN:
(纸本)3540660194
We study the problem of optimizing over the set of all combinatorial embeddings of a given planar graph. Our objective function prefers certain cycles of G as face cycles in the embedding. the motivation for studying this problem arises in graph drawing, where the chosen embedding has an important influence on the aesthetics of the drawing. We characterize the set of all possible embeddings of a given biconnected planar graph G by means of a system of linear inequalities with {0, 1}-variables corresponding to the set of those cycles in G which can appear in a combinatorial embedding. this system of linear inequalities can be constructed recursively using SPQR-trees and a new splitting operation. Our computational results on two benchmark sets of graphs are surprising: the number of variables and constraints seems to grow only linearly withthe size of the graphs although the number of embeddings grows exponentially. For all tested graphs (up to 500 vertices) and linear objective functions, the resulting integer linear programs could be generated within 10 minutes and solved within two seconds on a Sun Enterprise 10000 using CPLEX.
作者:
Sebo, ACNRS
Lab Leibniz IMAG Grenoble France Kyoto Univ
Math Sci Res Inst Kyoto 60601 Japan
We study simplices whose vertices lie on a lattice and have no other lattice points. Such 'empty lattice simplices' come up in the theory of integerprogramming, and in some combinatorial problems. they have b...
详细信息
ISBN:
(纸本)3540660194
We study simplices whose vertices lie on a lattice and have no other lattice points. Such 'empty lattice simplices' come up in the theory of integerprogramming, and in some combinatorial problems. they have been investigated in various contexts and under varying terminology by Reeve, White, Scarf, Kannan and Lovasz, Reznick, Kantor, Naase and Ziegler, etc. Can the 'emptiness' of lattice simplices be 'well-characterized' ? Is their 'lattice-width' small ? Do the integer points of the parallelepiped they generate have a particular structure ? the 'good characterization' of empty lattice simplices occurs to be open in general ! We provide a polynomial algorithm for deciding when a given integer 'knapsack' or 'partition' lattice simplex is empty. More generally, we ask for a characterization of linear inequalities satisfied by the lattice points of a lattice parallelepiped. We state a conjecture about such inequalities, prove it for n less than or equal to 4, and deduce several variants of classical results of Reeve, White and Scarf characterizing the emptiness of small dimensional lattice simplices. For instance, a three dimensional integer simplex is empty if and only if all its faces have width 1. Seemingly different characterizations can be easily proved from one another using the Hermite normal form. In fixed dimension the width of polytopes can be computed in polynomial time (see the simple integerprogramming formulation of Naase and Ziegler). We prove that it is already NP-complete to decide whether the width of a very special class of integer simplices is 1, and we also provide for every n greater than or equal to 3 a simple example of n-dimensional empty integer simplices of width n - 2, improving on earlier bounds.
the Chvatal rank of an inequality ax less than or equal to b with integral components and valid for the integral hull of a polyhedron P, is the minimum number of rounds of Gomory-Chvatal cutting planes needed to obtai...
详细信息
ISBN:
(数字)9783540487777
ISBN:
(纸本)3540660194
the Chvatal rank of an inequality ax less than or equal to b with integral components and valid for the integral hull of a polyhedron P, is the minimum number of rounds of Gomory-Chvatal cutting planes needed to obtain the given inequality. the Chvatal rank is st most one if b is the integral part of the optimum value z(a) of the linear program max{ax : x is an element of P}. We show that, contrary to what was stated or implied by other authors, the converse to the latter statement, namely, the Chvatal rank is at least two if b is less than the integral part of z(a), is not true in general. We establish simple conditions for which this implication is valid, and apply these conditions to several classes of facet-inducing inequalities for travelling salesman polytopes.
In this paper the symmetric traveling salesman problem (STSP) is modeled as a problem of discrete semidefinite programming. A class of semidefinite relaxations of STSP model is defined and two variants of a branch-and...
详细信息
At the ipco VI conference Cornuéjols and Dawande proposed a set of 0-1 linear programming instances that proved to be very hard to solve by traditional methods, and in particular by linear programming based branc...
详细信息
Gomory’s and Chvátal’s cutting-plane procedure proves recursively the validity of linear inequalities for the integer hull of a given polyhedron. the number of rounds needed to obtain all valid inequalities is ...
详细信息
暂无评论