Browsing by Subject "Facets"

Now showing 1 - 3 of 3

Open Access
The integer knapsack cover polyhedron
(Society for Industrial and Applied Mathematics, 2007) Yaman, H.
We study the integer knapsack cover polyhedron which is the convex hull of the set of vectors x ∈ ℤ+ n that satisfy C T x ≥ b, with C ∈ ℤ++ n and 6 ∈ ℤ++. We present some general results about the nontrivial facet-defining inequalities. Then we derive specific families of valid inequalities, namely, rounding, residual capacity, and lifted rounding inequalities, and identify cases where they define facets. We also study some known families of valid inequalities called 2-partition inequalities and improve them using sequence-independent lifting.
Open Access
k-node-disjoint hop-constrained survivable networks: polyhedral analysis and branch and cut
(Springer-Verlag France, 2018) Diarrassouba, I.; Mahjoub, M.; Mahjoub, A. R.; Yaman, Hande
Given a graph with weights on the edges, a set of origin and destination pairs of nodes, and two integers L ≥ 2 and k ≥ 2, the k-node-disjoint hop-constrained network design problem is to find a minimum weight subgraph of G such that between every origin and destination there exist at least k node-disjoint paths of length at most L. In this paper, we consider this problem from a polyhedral point of view. We propose an integer linear programming formulation for the problem for L ∈{2,3} and arbitrary k, and investigate the associated polytope. We introduce new valid inequalities for the problem for L ∈{2,3,4}, and give necessary and sufficient conditions for these inequalities to be facet defining. We also devise separation algorithms for these inequalities. Using these results, we propose a branch-and-cut algorithm for solving the problem for both L = 3 and L = 4 along with some computational results.
Open Access
Survivability in hierarchical telecommunications networks under dual homing
(Institute for Operations Research and the Management Sciences (I N F O R M S), 2014) Karaşan, O. E.; Mahjoub, A. R.; Özkök, O.; Yaman, H.
The motivation behind this study is the essential need for survivability in the telecommunications networks. An optical signal should find its destination even if the network experiences an occasional fiber cut. We consider the design of a two-level survivable telecommunications network. Terminals compiling the access layer communicate through hubs forming the backbone layer. To hedge against single link failures in the network, we require the backbone subgraph to be two-edge connected and the terminal nodes to connect to the backbone layer in a dual-homed fashion, i.e., at two distinct hubs. The underlying design problem partitions a given set of nodes into hubs and terminals, chooses a set of connections between the hubs such that the resulting backbone network is two-edge connected, and for each terminal chooses two hubs to provide the dual-homing backbone access. All of these decisions are jointly made based on some cost considerations. We give alternative formulations using cut inequalities, compare these formulations, provide a polyhedral analysis of the smallsized formulation, describe valid inequalities, study the associated separation problems, and design variable fixing rules. All of these findings are then utilized in devising an efficient branch-and-cut algorithm to solve this network design problem.