Pasquale Avella

Computational study of large-scale p -Median problems

Given a directed graph G(V,A), the p-Median problem consists of determining p nodes (the median nodes) minimizing the total distance from the other nodes of the graph. We present a Branch-and-Cut-and-Price algorithm yielding provably good solutions for instances with |V|≤3795. Key ingredients of the algorithm are a delayed column-and-row generation technique, exploiting the special structure of the formulation, to solve the LP-relaxation, and cutting planes to strengthen the formulation and limit the size of the enumeration tree.

Solving a fuel delivery problem by heuristic and exact approaches

Abstract In this paper we study the case of a company that delivers different types of fuel to a set of fuel pumps. The company has one warehouse and supplies the pumps by a fleet of trucks with several tanks of differing capacities. The company’s aim is to satisfy the orders using the available resources (trucks and drivers) with the minimum total travel cost for delivery. The problem has been formulated as a Set Partitioning model, solved by a Branch-and-Price algorithm. A fast combinatorial heuristic was adopted both to find a good feasible solution very quickly and to provide an initial set of columns for the Branch-and-Price algorithm. Computational results are reported. The exact approach shows low computation time for the real instances provided by the company.

On the p-Median polytope

Abstract.The p-Median problem defined on a complete directed graph with n nodes (

Metric inequalities and the Network Loading Problem

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A Computational Study of a Cutting Plane Algorithm for University Course Timetabling

n(V,A)) asks for a subset T⊆V of cardinality p and such that the weight of n-p arcs going from T to every node of V∖T, is minimized. The p-Median polytope Mn-p(

Some personal views on the current state and the future of Locational Analysis

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An effective heuristic for large-scale capacitated facility location problems

n(V,A)) is the convex hull of the incidence vectors of all the subsets of n-p arcs in A leaving a set T⊆V of cardinality p and entering in every node of V∖P.In this paper we show that the polytope Mn-p(

A computational study of exact knapsack separation for the generalized assignment problem

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A computational study of local search algorithms for Italian high-school timetabling

n(V,A)) is an “integral slice” of the Stable Set polytope STAB(Gn) associated with a suitable graph Gn(X,J) (i.e. is the convex hull of the integral points in the intersection of STAB(Gn) with the hyperplane ∑i∈Xxi=n-p). This allows us to define a very general class of facet-defining valid inequalities of Mn-p(

A cutting plane algorithm for the capacitated facility location problem

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