Maddalena Nonato

Tackling electrosmog in completely configured 3G networks by parallel cooperative meta-heuristics

The high quality standards required by third-generation systems can be reached only by way of a careful tuning of all the parameters of antenna configurations. However, concerns about exposure to electromagnetic fields should also be taken into account when designing telecommunication networks. In this article we investigate how parallel cooperative meta-heuristics provide the means to achieve both goals: devising a complete network configuration that meets coverage and service quality constraints, and minimizing electromagnetic field levels

Demand Adaptive Systems: Some Proposals on Flexible Transit1

Traditional public transport systems are evolving towards more flexible organizations in order to capture additional demand and reduce operational costs. Such a trend calls for new models and tools to support the management of new services that make use of public facilities to meet individual need.

An asymmetric vehicle routing problem arising in the collection and disposal of special waste

Abstract In this paper we consider a particular pick-up and delivery vehicle routing problem, with unit vehicle capacity and possible compatibility constraints between consecutive operations. The problem arises in the collection and disposal of bulky recyclable waste, where containers of different types, used to collect different waste materials, must be picked-up to be emptied at suitable disposal plants and replaced by empty containers alike. Disposal plants depend on the material and are located in different sites. Here we provide a graph model based on an Asymmetric Vehicle Routing formulation and discuss heuristic algorithms. Preliminary computational results obtained on real data are reported.

Meta-Heuristics for a Class of Demand-Responsive Transit Systems

The demand-adaptive systems studied in this paper attempt to offer demand-responsive services within the framework of traditional scheduled bus transportation: Users call to request service between two given points and, in so doing, induce detours in the vehicle routes; at the same time, though, a given set of compulsory stops is always served according to a predefined schedule, regardless of the current set of active requests. The model developed to select requests and determine the routing of the vehicle yields a difficult formulation but with a special structure that may be used to develop efficient algorithms. In this paper, we develop, test, and compare several solution strategies for the single line-single vehicle problem that belong to two general meta-heuristic classes, memory-enhanced greedy randomized multistart constructive procedures, and tabu search methods. Hybrid meta-heuristics combining the two methods are also analyzed.

Adaptive Memory Programming for a Class of Demand Responsive Transit Systems

In this paper we discuss Demand Adaptive Systems (DAS) which are intended as a hybrid public transportation system that integrates traditional bus transportation and on demand service, DAS lines regularly serve a given set of compulsory stops according to a predefined schedule and regardless of current demand. Between a compulsory stop and the next, optional stops can be activated on demand. Vehicles have to be rerouted and scheduled in order to satisfy as many requests as possible, complying with passage-time constraints at compulsory stops. This paper provides a general description of DAS, and discusses potential applications and solution methods, emphasizing differences and analogies with classical Demand Responsive Systems. The particular mathematical structure of DAS requires innovative solution methods even when addressing its simplest version, the single vehicle, single line case. An efficient meta-heuristic algorithm based on adaptive memory ideas has been developed for this case. The method integrates sophisticated mathematical programming tools into a tabu search framework, taking advantage of the particular structure of the problem. The methodology is briefly discussed and experimental results are presented for the single line case. We show that the basic case can be efficiently solved, thus providing efficient algorithmic building blocks for more comprehensive approaches tackling the general case.

Optimal placement of valves in a water distribution network with CLP(FD)

This paper presents a new application of logic programming to a real-life problem in hydraulic engineering. The work is developed as a collaboration of computer scientists and hydraulic engineers, and applies Constraint Logic Programming to solve a hard combinatorial problem. This application deals with one aspect of the design of a water distribution network, i.e., the valve isolation system design. We take the formulation of the problem by Giustolisi and Savic (2008 Optimal design of isolation valve system for water distribution networks. In Proceedings of the 10th Annual Water Distribution Systems Analysis Conference WDSA2008 , J. Van Zyl, A. Ilemobade, and H. Jacobs, Eds.) and show how, thanks to constraint propagation, we can get better solutions than the best solution known in the literature for the Apulian distribution network. We believe that the area of the so-called hydroinformatics can benefit from the techniques developed in Constraint Logic Programming and possibly from other areas of logic programming, such as Answer Set Programming.

Orthogonal drawings of graphs with vertex and edge labels

This paper studies the problem of computing orthogonal drawings of graphs with labels on vertices and edges. Our research is mainly motivated by Software Engineering and Information Systems domains, where tools like UML diagrams and ER-diagrams are considered fundamental for the design of sophisticated systems and/or complex data bases collecting enormous amount of information. A label is modeled as a rectangle of prescribed width and height and it can be associated with either a vertex or an edge. Our drawing algorithms guarantee no overlaps between labels, vertices, and edges and take advantage of the information about the set of labels to compute the geometry of the drawing. Several additional optimization goals are taken into account. Namely, the labeled drawing can be required to have either minimum total edge length, or minimum width, or minimum height, or minimum area among those preserving a given orthogonal representation. All these goals lead to NP-hard problems. We present MILP models to compute optimal drawings with respect to the first three goals and an exact algorithm that is based on these models to compute a labeled drawing of minimum area. We also present several heuristics for computing compact labeled orthogonal drawings and experimentally validate their performances, comparing their solutions against the optimum.

An ASP approach for the valves positioning optimization in a water distribution system

Positioning of valves is a real-life issue in Water Distribution System design and, currently, it is usually addressed by hand by hydraulic engineers, or by means of genetic algorithms, that give no assurance of optimality. Since a given valves placement identifies a sectorization of the WDS in several isolable portions, the valves positioning problem can be seen as a variant of the well known graph partitioning, which is a hard combinatorial problem. [2] showed recently that Computational Logic can provide technologies and techniques that can be exploited to model and achieve the optimal partition of the water network (i.e., the optimal positioning of valves). In particular, they tackled the optimization of the valves positioning through a two player game model, giving a Constraint Logic Programming formalization to solve it effectively. The aim of this paper, instead, is to investigate the potential of Answer Set Programming in this practical application; evaluation is in terms both of language expressivity and solving efficiency. Results are discussed for different ASP models and a comparison with the CLP(FD) technique shown by [2] will be given.

On Girth Conditioning for Low-Density Parity-Check Codes

Low-density parity-check (LDPC) codes are gaining interest for high data rate applications in both terrestrial and spatial communications. They can be designed and studied through a bipartite graph whose characteristics affect the performance. This paper proposes a low-complexity method to improve the performance of LDPC codes by selectively removing some cycles from the associated bipartite graph. The method is based on a modified version of the breadth first search (BFS) algorithm that we call modified BFS (MBFS), which is applied to find cycles, and a greedy procedure to eliminate them. Throughout the paper we will give a detailed description of the algorithm proposed and analytically study its complexity. Simulation results show that this girth conditioning method applied to some classes of codes, whose structure allows further optimization, can lead to a significative complexity reduction and a performance improvements with respect to other methods.

Design technology for fault-free and maximally-parallel wavelength-routed optical networks-on-chip

The recent interest in emerging interconnect technologies is bringing the issue of a proper EDA support for them to the forefront, so to tackle the design complexity. A relevant case study is provided by wavelength-routed optical NoCs (WRONoCs), which add communication performance guarantees to the typical latency, throughput and power benefits of an optical link, thus providing an appealing technology for the photonic integration of high-end embedded systems. Typically, only abstract WRONoC models are considered to figure out architecture-level performance, and logic connectivity patterns for the quantification of the required signal strength (i.e., static power). However, this design practice overlooks the needed refinement step, where key physical parameters are assigned such as wavelengths of the optical channels, and size of the optical filters. This step is unfortunately not decoupled from the architectural evaluation, since its main constraint (i.e., avoiding routing faults) turns out to be a key limiter for both the network scale and the achievable communication parallelism. By proposing a formal methodology to select WRONoC parameters while avoding the routing fault concern, this paper aims at maximizing the levels of connectivity and/or of bit parallelism that WRONoCs can achieve, while relating their upper bounds to the uncertainty of the manufacturing process.