Daniele Ferone

Hybrid Metaheuristics for the Far From Most String Problem

Among the sequence selection and comparison problems, the Far From Most String Problem (FFMSP) is one of the computationally hardest with applications in several fields, including molecular biology where one is interested in creating diagnostic probes for bacterial infections or in discovering potential drug targets.

A biased-randomized simheuristic for the distributed assembly permutation flowshop problem with stochastic processing times

Abstract Modern manufacturing systems are composed of several stages. We consider a manufacturing environment in which different parts of a product are completed in a first stage by a set of distributed flowshop lines, and then assembled in a second stage. This is known as the distributed assembly permutation flowshop problem (DAPFSP). This paper studies the stochastic version of the DAPFSP, in which processing and assembly times are random variables. Besides minimizing the expected makespan, we also discuss the need for considering other measures of statistical dispersion in order to account for risk. A hybrid algorithm is proposed for solving this NP -hard and stochastic problem. Our approach integrates biased randomization and simulation techniques inside a metaheuristic framework. A series of computational experiments contribute to illustrate the effectiveness of our approach.

The constrained shortest path tour problem

In this paper, we study the constrained shortest path tour problem. Given a directed graph with non-negative arc lengths, the aim is to find a single-origin single-destination shortest path, which needs to cross a sequence of node subsets that are given in a fixed order. The subsets are disjoint and may be of different size. In addition, it is required that the path does not include repeated arcs.Theoretical properties of the problem are studied, proving that it belongs to the complexity class NP-complete. To exactly solve it, a Branch & Bound method is proposed. Given the problem hardness, a Greedy Randomized Adaptive Search Procedure is also developed to find near-optimal solutions for medium to large scale instances.Extensive computational experiments, on a significant set of test problems, are carried out in order to empirically evaluate the performance of the proposed approaches. The computational results show that the Greedy Randomized Adaptive Search Procedure is effective in finding optimal or near optimal solutions in very limited computational time. HighlightsA constrained version of the Shortest Path Tour Problem is addressed.Its theoretical properties are analyzed: the problem belongs to the NP-complete class.A Branch & Bound (B&B) and a GRASP are proposed for its solution.The B&B can be used to solve only small size instances.The GRASP is able to address instances of up to 400 nodes in less than 200s.

A New Local Search for the p -Center Problem Based on the Critical Vertex Concept

For the p-center problem, we propose a new smart local search based on the critical vertex concept and embed it in a GRASP framework. Experimental results attest the robustness of the proposed search procedure and confirm that for benchmark instances it converges to optimal or near/optimal solutions faster than the best known state-of-the-art local search.

Combining simulation with a GRASP metaheuristic for solving the permutation flow-shop problem with stochastic processing times

Greedy Randomized Adaptive Search Procedures (GRASP) are among the most popular metaheuristics for the solution of combinatorial optimization problems. While GRASP is a relatively simple and efficient framework to deal with deterministic problem settings, many real-life applications experience a high level of uncertainty concerning their input variables or even their optimization constraints. When properly combined with the right metaheuristic, simulation (in any of its variants) can be an effective way to cope with this uncertainty. In this paper, we present a simheuristic algorithm that integrates Monte Carlo simulation into a GRASP framework to solve the permutation flow shop problem (PFSP) with random processing times. The PFSP is a well-known problem in the supply chain management literature, but most of the existing work considers that processing times of tasks in machines are deterministic and known in advance, which in some real-life applications (e.g., project management) is an unrealistic assumption.

A new GRASP metaheuristic for biclustering of gene expression data

The term biclustering stands for simultaneous clustering of both genes and conditions. This task has generated considerable interest over the past few decades, particularly related to the analysis of high-dimensional gene expression data in information retrieval, knowledge discovery, and data mining [1]. Since the problem has been shown to be NP-complete, we have recently designed and implemented a GRASP metaheuristic [2,3,4]. The greedy criterion used in the construction phase uses the Euclidean distance to build spanning trees of the graph representing the input data matrix. Once obtained a complete solution, the local search procedure tries to both enlarge the current solution and to improve its H-score exchanging rows and columns. The proposed approach has been tested on 5 synthetic datasets [5]: 1) constant biclusters; 2) constant, upregulated biclusters; 3) shiftscale biclusters; 4) shift biclusters, and 5) scale biclusters. Compared with state-of-the-art competitors, its behaviour is excellent on shift datasets and is very good on all other datasets except for scaled ones. In order to improve its behaviour on scaled data as well and to reduce running times, we have designed and preliminarily tested a variant of the existing GRASP, whose local search phase returns an approximate local optimal solution. The resulting algorithm promises to be a more efficient, general, and robust method for the biclustering of all kinds of possible biological data.

Enhancing and extending the classical GRASP framework with biased randomisation and simulation

Abstract Greedy Randomised Adaptive Search Procedure (GRASP) is one of the best-known metaheuristics to solve complex combinatorial optimisation problems (COPs). This paper proposes two extensions of the typical GRASP framework. On the one hand, applying biased randomisation techniques during the solution construction phase enhances the efficiency of the GRASP solving approach compared to the traditional use of a restricted candidate list. On the other hand, the inclusion of simulation at certain points of the GRASP framework constitutes an efficient simulation–optimisation approach that allows to solve stochastic versions of COPs. To show the effectiveness of these GRASP improvements and extensions, tests are run with both deterministic and stochastic problem settings related to flow shop scheduling, vehicle routing, and facility location.

A GRASP for the Minimum Cost SAT Problem

A substantial connection exists between supervised learning from data represented in logic form and the solution of the Minimum Cost Satisfiability Problem (MinCostSAT). Methods based on such connection have been developed and successfully applied in many contexts. The deployment of such methods to large-scale learning problem is often hindered by the computational challenge of solving MinCostSAT, a problem well known to be NP-complete. In this paper, we propose a GRASP-based metaheuristic designed for such problem, that proves successful in leveraging the very distinctive structure of the MinCostSAT problems arising in supervised learning. The algorithm is equipped with an original stopping criterion based on probabilistic assumptions which results very effective for deciding when the search space has been explored enough. Although the proposed solver may approach MinCostSAT of general form, in this paper we limit our analysis to some instances that have been created from artificial supervised learning problems, and show that our method outperforms more general purpose well established solvers.

On the fast solution of the p-center problem

The p-center problem is one of the classical facility location problems. It finds applications in several different fields, including network planning and network optimization. Due to the increasing of bandwidth requirements, telecommunication operators are renewing the access networks in favoring of optical networks. Generally, the design of access network consists in determining the location of physical networks from a given list of potential locations. Indeed, in order to ensure the efficient usage of a limited number of resources, the identification of facility locations plays a central role. In this paper, we formally define the p-center problem, briefly survey the most efficient state of the art algorithms to approach it, and describe a new smart and fast local search able to find optimal or near-optimal solutions. We also discuss and analyze the results of our extensive computational experience on benchmark instances and on optical network instances.

SHORTEST PATHS ON DYNAMIC GRAPHS: A SURVEY

This paper provides an overview of the state-of-the art and the current research trends concerning shortest paths problem on dynamic graphs. The discussion is divided in two main topics: reoptimization and time-dependent shortest paths. Reoptimization consists in the solution of a sequence of shortest path problems in which each instance slightly differs from the previous one. The reoptimization tackles this problem wisely using information stored in an optimal solution previously computed. On the other hand, shortest path problems on time-dependent graphs are characterized by a weight function which not only depends upon the arcs but changes in time according to a certain time horizon.