The optimal track allocation problem (OPTRA) is to find, in a given railway network, a conflict free set of train routes of maximum value. We study two types of integer programming formulations for this problem: a standard formulation that models block conflicts in terms of packing constraints, and a novel formulation of the ‘extended’ type that is based on additional ‘configuration’ variables....

We consider the problem of obtaining the approximate maximum a posteriori estimate of a discrete random field characterized by pairwise potentials that form a truncated convex model. For this problem, we propose an improved st-MINCUT based move making algorithm. Unlike previous move making approaches, which either provide a loose bound or no bound on the quality of the solution (in terms of the...

In the Tree Augmentation problem the goal is to augment a tree T by a minimum size edge set F from a given edge set E such that T ∪ F is 2-edge-connected. The best approximation ratio known for the problem is 1.5. In the more general Weighted Tree Augmentation problem, F should be of minimum weight. Weighted Tree Augmentation admits several 2-approximation algorithms w.r.t. the standard cut-LP ...

We propose exact hybrid methods based on integer linear programming and constraint programming for an integrated employee timetabling and production scheduling problem. Each method we investigate uses a constraint programming (CP) formulation associated with a linear programming (LP) relaxation. Under a CP framework, the LP-relaxation is integrated into a global constraint using in addition red...

We study a class of models, known as overlay optimization problems, with a "base" subproblem and an "overlay" subproblem, linked by the requirement that the overlay solution be contained in the base solution. In some telecommunication settings, a feasible base solution is a spanning tree and the overlay solution is an embedded Steiner tree (or an embedded path). For the general overlay optimiza...

In this paper we describe a two-stage optimization model for determining robust rolling stock circulations for passenger trains. Here robustness means that the rolling stock circulations can better deal with large disruptions of the railway system. The two-stage optimization model is formulated as a large Mixed-Integer Linear Programming model. We first use Benders decomposition to determine op...

JOINT LINK/PACKET SCHEDULING, RATE ALLOCATION AND ROUTING OPTIMIZATION IN STDMA BASED WIRELESS MESH NETWORKS Ahmet Emrah SEZGİN M.S. in Electrical and Electronics Engineering Supervisor: Assoc. Prof. Dr. Ezhan KARAŞAN August 2009 Wireless Mesh Networks (WMN) are a promising solution for next generation wireless access networks since they cherish benefits of having a reliable backbone in an ad h...

In this paper we introduce a GRASP for the solution of general linear integer programs (IP). The strategy is based on the separation of the set of variables into the integer subset and the continuous subset. The procedure starts by solving the linear programming (LP) relaxation of the problem. Values for the integer variables are then chosen, through a randomised greedy construction heuristic b...

MPEG-4 is the first visual coding standard that allows coding of scenes as a collection of individual audio-visual objects. We present mathematical formulations for modeling object-based scalability and some functionalities that it brings with it. Our goal is to study algorithms that aid in semi-automating the authoring and subsequent selective addition/dropping of objects from a scene to provi...

In this paper, we provide a new class of randomized approximation algorithms for parallel machine scheduling problems. The most general model we consider is scheduling unrelated machines with release dates (or even network scheduling) so as to minimize the average weighted completion time. We introduce an LP relaxation in time-indexed variables for this problem. The crucial idea to derive appro...