Andrea Peano

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.

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.

aspartame : Solving Constraint Satisfaction Problems with Answer Set Programming

Encoding finite linear CSPs as Boolean formulas and solving them by using modern SAT solvers has proven to be highly effective by the award-winning sugar system. We here develop an alternative approach based on ASP that serves two purposes. First, it provides a library for solving CSPs as part of an encompassing logic program. Second, it furnishes an ASP-based CP solver similar to sugar. Both tasks are addressed by using first-order ASP encodings that provide us with a high degree of flexibility, either for integration within ASP or for easy experimentation with different implementations. When used as a CP solver, the resulting system aspartame re-uses parts of sugar for parsing and normalizing CSPs. The obtained set of facts is then combined with an ASP encoding that can be grounded and solved by off-the-shelf ASP systems. We establish the competitiveness of our approach by empirically contrasting aspartame and sugar.

A Bilevel Mixed Integer Linear Programming Model for Valves Location in Water Distribution Systems

The positioning of valves on the pipes of a Water Distribution System (WDS) is a core decision in the design of the isolation system of a WDS. When closed, valves permit to isolate a small portion of the network, so called a sector, which can be de-watered for maintenance purposes at the cost of a supply disruption. However, valves have a cost so their number is limited, and their position must be chosen carefully in order to minimize the worst-case supply disruption which may occur during pipe maintenance. Supply disruption is usually measured as the undelivered user demand. When a sector is isolated by closing its boundary valves, other portions of the network may become disconnected from the reservoirs as a secondary effect, and experience supply disruption as well. This induced isolation must be taken into account when computing the undelivered demand induced by a sector isolation. While sector topology can be described in terms of graph partitioning, accounting for induced undelivered demand requires network flow modeling. The aim of the problem is to locate a given number of valves at the extremes of the network pipes so that the maximum supply disruption is minimized. We present a Bilevel Mixed Integer Linear Programming (MILP) model for this problem and show how to reduce it to a single level MILP by exploiting duality. Computational results on a real case study are presented, showing the effectiveness of the approach.

Scheduling countermeasures to contamination events by genetic algorithms

This paper heuristically tackles a challenging scheduling problem arising in the field of hydraulic distribution systems in case of a contamination event, that is, optimizing the scheduling of a set of tasks so that the consumed volume of contaminated water is minimized. Each task consists of manually activating a given device, located on the hydraulic network of the water distribution system. In practice, once contamination has been detected, a given number of response teams move along the network to operate each device on site. The consumed volume of contaminated water depends on the time at which each device is operated, according to complex hydraulic laws, so that the value associated to each schedule must be evaluated by a hydraulic simulation.We explore the potentials of Genetic Algorithms as a viable tool for tackling this optimization-simulation problem. We compare different encodings and propose ad hoc crossover operators that exploit the combinatorial structure of the feasible region, featuring hybridization with Mixed Integer Linear Programming.Extensive computational results are provided for a real life hydraulic network of average size, showing the effectiveness of the approach. Indeed, we greatly improve upon common sense inspired solutions which are commonly adopted in practice.

A network model for routing-fault-free wavelength selection in WRONoCs design

Abstract Emerging technologies in on-chip communication domain bring about new combinatorial optimization problems at design automation. We address the Wavelength Selection Problem in Wavelength-Routed Optical Networks-on-Chip (WRONoCs), where wavelengths act as signal carriers for initiator-to-target communication, so that signals are the least interfering and routing faults are prevented. We present this novel engineering problem and model it as a constrained shortest path on acyclic networks, propose a graph-based mathematical formulation and an iterative procedure on incremental graphs to solve the model on realistic data.

Logic programming approaches for routing fault-free and maximally parallel wavelength-routed optical networks-on-chip (Application paper)

One promising trend in digital system integration consists of boosting on-chip communication performance by means of silicon photonics, thus materializing the so-called Optical Networks-on-Chip (ONoCs). Among them, wavelength routing can be used to route a signal to destination by univocally associating a routing path to the wavelength of the optical carrier. Such wavelengths should be chosen so to minimize interferences among optical channels and to avoid routing faults. As a result, physical parameter selection of such networks requires the solution of complex constrained optimization problems. In previous work, published in the proceedings of the International Conference on Computer-Aided Design, we proposed and solved the problem of computing the maximum parallelism obtainable in the communication between any two endpoints while avoiding misrouting of optical signals. The underlying technology, only quickly mentioned in that paper, is Answer Set Programming (ASP). In this work, we detail the ASP approach we used to solve such problem. Another important design issue is to select the wavelengths of optical carriers such that they are spread across the available spectrum, in order to reduce the likelihood that, due to imperfections in the manufacturing process, unintended routing faults arise. We show how to address such problem in Constraint Logic Programming on Finite Domains (CLP(FD)). This paper is under consideration for possible publication on Theory and Practice of Logic Programming.

Path Relinking for a Constrained Simulation-Optimization Team Scheduling Problem Arising in Hydroinformatics

We apply Path Relinking to a real life constrained optimization problem concerning the scheduling of technicians due to activate on site devices located on a water distribution network in case of a contamination event, in order to reduce the amount of consumed contaminated water. Teams travel on the road network when moving from one device to the next, as in the Multiple Traveling Salesperson Problem. The objective, however, is not minimizing travel time but the minimization of consumed contaminated water. This is computed through a computationally demanding simulation given the devices activation times. We propose alternative Path Relinking search strategies exploiting time-based and precedence-based neighborhoods, and evaluate the improvement gained by coupling Path Relinking with state of the art, previously developed, hybrid Genetic Algorithms. Experimental results on a real network are provided to support the efficacy of the methodology.

An ASP Approach for the Optimal Placement of the Isolation Valves in a Water Distribution System

My Ph.D. Thesis relates to real-life optimization problems in the hydraulic engineering field. More precisely, with the collaboration of computer scientists, operational researchers and hydraulic engineers, I investigate and exploit potentialities of various Operational Research and Artificial Intelligence techniques in order to achieve good (and, whenever possible, optimal) solutions for those particular design issues of the urban hydraulic network that can be effectively modelled as known combinatorial optimization problems. Furthermore, suchdesign issues often require to devise new specialized variants of the known combinatorial optimization problems.