Ali Ridha Mahjoub

Bio: Ali Ridha Mahjoub is an academic researcher from Paris Dauphine University. The author has contributed to research in topics: Polytope & Birkhoff polytope. The author has an hindex of 20, co-authored 79 publications receiving 1502 citations. Previous affiliations of Ali Ridha Mahjoub include IBM & University of Paris.

On the cut polytope

Abstract: The cut polytopeP C (G) of a graphG=(V, E) is the convex hull of the incidence vectors of all edge sets of cuts ofG. We show some classes of facet-defining inequalities ofP C (G). We describe three methods with which new facet-defining inequalities ofP C (G) can be constructed from known ones. In particular, we show that inequalities associated with chordless cycles define facets of this polytope; moreover, for these inequalities a polynomial algorithm to solve the separation problem is presented. We characterize the facet defining inequalities ofP C (G) ifG is not contractible toK 5. We give a simple characterization of adjacency inP C (G) and prove that for complete graphs this polytope has diameter one and thatP C (G) has the Hirsch property. A relationship betweenP C (G) and the convex hull of incidence vectors of balancing edge sets of a signed graph is studied.

A branch-and-cut algorithm for the k-edge connected subgraph problem

Abstract: In this article, we consider the k-edge connected subgraph problem from a polyhedral point of view. We introduce further classes of valid inequalities for the associated polytope and describe sufficient conditions for these inequalities to be facet defining. We also devise separation routines for these inequalities and discuss some reduction operations that can be used in a preprocessing phase for the separation. Using these results, we develop a Branch-and-Cut algorithm and present some computational results. © 2009 Wiley Periodicals, Inc. NETWORKS, 2010

Two-edge connected spanning subgraphs and polyhedra

Abstract: This paper studies the problem of finding a two-edge connected spanning subgraph of minimum weight. This problem is closely related to the widely studied traveling salesman problem and has applications to the design of reliable communication and transportation networks. We discuss the polytope associated with the solutions to this problem. We show that when the graph is series-parallel, the polytope is completely described by the trivial constraints and the so-called cut constraints. We also give some classes of facet defining inequalities of this polytope when the graph is general.

Facets of the Bipartite Subgraph Polytope

Abstract: The bipartite subgraph polytope PBG of a graph G = [V, E] is the convex hull of the incidence vectors of all edge sets of bipartite subgraphs of G. We show that all complete subgraphs of G of odd order and all so-called odd bicycle wheels contained in G induce facets of PBG. Moreover, we describe several methods with which new facet defining inequalities of PBG can be constructed from known ones. Examples of these methods are contraction of node sets in odd complete subgraphs, odd subdivision of edges, certain splittings of nodes, and subdivision of all edges of a cut. Using these methods we can construct facet defining inequalities of PBG having coefficients of order |V|2.

Compositions of Graphs and Polyhedra II: Stable Sets

Abstract: A graph $G$ with a two-node cutset decomposes into two pieces. A technique to describe the stable set polytope for $G$ based on stable set polytopes associated with the pieces is studied. This gives a way to characterize this polytope for classes of graphs that can be recursively decomposed. This also gives a procedure to describe new facets of this polytope. A compact system for the stable set problem in series-parallel graphs is derived. This technique is also applied to characterize facet-defining inequalities for graphs with no $K_{5}\e$ minor. The stable set problem is polynomially solvable for this class of graphs. Compositions of $h$-perfect graphs are also studied.

Routing, Flow, And Capacity Design In Communication And Computer Networks

Abstract: In network design, the gap between theory and practice is woefully broad. This book narrows it, comprehensively and critically examining current network design models and methods. You will learn where mathematical modeling and algorithmic optimization have been under-utilized. At the opposite extreme, you will learn where they tend to fail to contribute to the twin goals of network efficiency and cost-savings. Most of all, you will learn precisely how to tailor theoretical models to make them as useful as possible in practice. Throughout, the authors focus on the traffic demands encountered in the real world of network design. Their generic approach, however, allows problem formulations and solutions to be applied across the board to virtually any type of backbone communication or computer network. For beginners, this book is an excellent introduction. For seasoned professionals, it provides immediate solutions and a strong foundation for further advances in the use of mathematical modeling for network design. (Less)

A survey on pickup and delivery problems: Part II: Transportation between pickup and delivery locations

Abstract: This paper is the second part of a comprehensive survey on pickup and delivery models. Basically, two problem classes can be distinguished. The first part dealt with the transportation of goods from the depot to linehaul customers and from backhaul customers to the depot. In this class four subtypes were considered, namely the Vehicle Routing Problem with Clustered Backhauls (VRPCB all linehauls before backhauls), the Vehicle Routing Problem with Mixed linehauls and Backhauls (VRPMB any sequence of linehauls and backhauls permitted), the Vehicle Routing Problem with Divisible Delivery and Pickup (VRPDDP customers demanding delivery and pickup service can be visited twice), and the Vehicle Routing Problem with Simultaneous Delivery and Pickup (VRPSDP customers demanding both services have to be visited exactly once). The second part now considers all those problems where goods are transported between pickup and delivery locations, denoted as Vehicle Routing Problems with Pickups and Deliveries (VRPPD). These are the Pickup and Delivery VRP (PDVRP unpaired pickup and delivery points), the classical Pickup and Delivery Problem (PDP paired pickup and delivery points), and the Dial-A-Ride Problem (DARP paired pickup and delivery points and user inconvenience taken into consideration). A single as well as a multi vehicle mathematical problem formulation for all three VRPPD types is given, and the respective exact, heuristic, and metaheuristic solution methods are discussed.