Julián Aráoz

Solving the Prize-collecting Rural Postman Problem

In this work we present an algorithm for solving the Prize-collecting Rural Postman Problem. This problem was recently defined and is a generalization of other arc routing problems like, for instance, the Rural Postman Problem. The main difference is that there are no required edges. Instead, there is a profit function on the edges that must be taken into account only the first time that an edge is traversed. The problem is modeled as a linear integer program where the system has an exponential number of inequalities. We propose a solution algorithm where iteratively we solve relaxed models with a small number of inequalities, that provide upper bounds, and we propose exact separation procedures for generating violated cuts when possible. We also propose a simple heuristic to generate feasible solutions that provide lower bounds at each iteration. We use a two-phase method with different solvers at each phase. Despite the difficulty of the problem, the numerical results from a series of computational experiments with various types of instances assess the good behavior of the algorithm. In particular, 75% of the instances were optimally solved with the LP relaxation of the model. The remaining instances were optimally solved on a second phase, most of them in small computation times.

Privatized rural postman problems

In this work we analyze the privatized rural postman problem which is the edge version of the traveling salesman problems with profits.The problem is defined on a undirected graph G(V, E) with a distinguished vertex d, called the Depot. There are two non-negative real functions on the edge set E, which define the value of a cycle in G: one is the profit function, b, and the other one is the cost function, c. They have different meanings when a cycle C traverses an edge e (possibly more than once), because we pay a cost ce every time e is traversed, but we collect the profit be only the first time e is traversed. The privatized rural postman problem is to find a cycle C*, passing through d and not necessarily simple, which maximizes the sum of the values of the edges traversed in C*. That is, maxC {Σe∈C (be - teCe)} where te is the number of times that edge e is traversed in C.We study some properties of the problem: we show that it is NP-hard, its relation with known and new problems, and special cases with good algorithms. We also analyze several integer linear systems of inequalities, which define the polyhedral structure of the problem, and we give dominance and preprocessing conditions. We finish with some remarks and comments about future research.

The Clustered Prize-Collecting Arc Routing Problem

Prize-collecting arc routing problems are arc routing problems where, in addition to the cost function, there is a profit function on the edges that must only be taken into account the first time that an edge is traversed. This work presents the clustered prize-collecting arc routing problem where there are clusters of arcs and it is required that all or none of the edges of a cluster be serviced. The paper studies properties and dominance conditions used for formulating the problem as a linear integer program. An exact algorithm for finding an optimal solution to the problem is also proposed. At the root node of the enumeration tree, the algorithm generates upper and lower bounds obtained from solving an iterative linear programming-based algorithm in which violated cuts are generated when possible. A simple heuristic that generates feasible solutions provides lower bounds at each iteration. The numerical results from a series of computational experiments with various types of instances illustrate the good behavior of the algorithm. Over 75% of the instances were solved at the root node, and the remaining instances were solved with a small additional computational effort.

GRASP and Path Relinking for the Clustered Prize-collecting Arc Routing Problem

The Clustered Prize-collecting Arc Routing Problem is an arc routing problem where each demand edge is associated with a profit which is collected once if the edge is serviced, independently of the number of times it is traversed. It is further required that if a demand edge is serviced, then all the demand edges of its component are also serviced.This paper presents GRASP and Path Relinking heuristics for the Clustered Prize-collecting Arc Routing Problem. For the constructive phase of the GRASP two different strategies are considered. One of them follows a bottom-up style whereas the other one is a top-down procedure. The best solutions obtained with both strategies are used as elite solutions for the Path Relinking. The results of extensive computational experiments are presented and analyzed.

Evolution of computing in spanish-speaking countries

Two decades ago, people used computers as an information resource for many fields. These fields include library information, climatic information, medicine, transportation schedules, banking, and other areas. The use of international networks at that time enabled people to communicate globally in a rapid and accurate fashion not only to experts, but to the public also. In regions such as South and Central America, however, the uses of information resources were not as widespread as they were in developed countries. Indeed, estimates showed that Latin America contained two percent of the world’s informatics equipment. At that time, computers appeared in commercial and governmental agencies as well as universities that used global networks such as the internet, BITNET, FidoNet, and other similar networks.

Human Resources Education in Computing at Simon Bolivar University, Venezuela

In this work we describe the efforts of the Computing Coordination at Simon Bolivar University, Venezuela, for forming Human Recourses in Computing at graduate and postgraduate levels in the years from 1972 to 1985. We also consider the background given by the Scientific Computer Program at the Calculus Institute, Buenos Aires University, that begun in 1962 and by the Computation Licentiate Program at Science Faculty, Venezuelan Central University, that begun in 1967. We close considering the impact that programs and professors from Simon Bolivar University have at national and regional levels.