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.Comment: Paper presented at the 33nd International Conference on Logic Programming (ICLP 2017), Melbourne, Australia, August 28 to September 1, 2017. 16 pages, LaTeX, 5 figure

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) 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.Comment: Best paper award at the 27th International Conference on Logic Programming - ICLP 2011; Theory and Practice of Logic Programming, (ICLP'11) Special Issue, volume 11, issue 4-5, 201

On Girth Conditioning for Low-Density Parity-Check Codes

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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

Improving Quality and Efficiency in Home Health Care: an application of Constraint Logic Programming for the Ferrara NHS unit

Although sometimes it is necessary, no one likes to stay in a hospital, and patients who need to stay in bed but do not require constant medical surveillance prefer their own bed at home. At the same time, a patient in a hospital has a high cost for the community, that is not acceptable if the patient needs service only a few minutes a day. For these reasons, the current trend in Europe and North-America is to send nurses to visit patients in their home: this choice reduces costs for the community and gives better quality of life to patients. On the other hand, it introduces the combinatorial problem of assigning patients to the available nurses in order to maximize the quality of service, without having nurses travel for overly long distances. In this paper, we describe the problem as a practical application of Constraint Logic Programming. We first introduce the problem, as it is currently addressed by the nurses in the National Health Service (NHS) in Ferrara, a mid-sized city in the North of Italy. Currently, the nurses solve the problem by hand, and this introduces several inefficiencies in the schedules. We formalize the problem, obtained by interacting with the nurses in the NHS, into a Constraint Logic Programming model. In order to solve the problem efficiently, we implemented a new constraint that tackles with the routing part of the problem. We propose a declarative semantics for the new constraint, and an implementation based on an external solver

Cycle-tourist network design

Among the most effective actions to promote functional cycling, i.e., cycling as a mean of transport, infrastructure design and planning are major topics. Much less attention has been dedicated to the design and deployment of bikeways devoted to recreational cycling, despite the role of cycle routes in promoting cycle tourism, and the effectiveness of cycle tourism in fostering sustainable and environmentally friendly economic growth, in addition to encouraging healthy life styles. In this paper we contribute to fill this gap: we propose a quantitative based methodology for designing a cycle-tourist network infrastructure intended to provide local administrators with a quantitative based decision support tool to optimally exploit the scarce public funding devoted to the project deployment. We consider as a case study the data of the Trebon region, in South Bohemia. Given the local points of attractions and a set of potential links which can be turned into cycle pathways against a little investment in addition to a set of links already fit for cyclists, a network of cycle routes that interconnects a set of pre selected gates must be designed, so that the total link refurbishment cost is budget compliant and the attractiveness of cycle itineraries from gate to gate supported by the infrastructure is maximized. In previous studies we showed how to compute a resource-constrained optimal path from origin to destination, which maximizes a utility function related to the attractiveness of the arcs and nodes along the path. In a later work we generalized the problem to the case of multiple users with different utility functions that must share the same monetary budget. Building on these results, in this paper we propose a heuristic solution approach for the network design problem, where routes connecting several origin destination pairs have to be designed, yielding a connected infrastructure which allows for further itineraries. We exploit the ability of modern solvers to quickly find solutions to the single-pair single-user aforementioned case to generate a pool of promising paths from gate to gate, according to different preferences and constraints. In a second step, the network is built by solving a second combinatorial optimization problem which selects a path for each pair of gates from the pool, to yield a budget compliant connected infrastructure. Finally, a post optimization step deletes redundant links, if any. The solution approach is validated by an experimental campaign performed on realistic data for the Trebon zone, in Southern Bohemia

Designing Optimal Routes for Cycle-tourists

AbstractBicycles are becoming an increasingly popular mean of transport. Being healthy and affordable, they provide a sustainable alternative way of movement, for both leisure and work commuting. In both cases demand increases when bike devoted tracks are available. Providing bike trails that connect touristic spots is a cheap way of increasing the appeal and promoting the development of those regions featuring beautiful landscapes, strong cultural traditions, and historical monuments within a small area. This is the case of the Trebon region, South Bohemia, whose local administrators face the problem of optimally investing scarce resources to set up a network of cycle-dedicated tracks, exploiting existing trails or by reconstruction works, turning gravel roads or unsurfaced forest tracks into paved bike trails. As a first step, we address the design of a single route, modeled as a path on a directed graph between two given nodes, maximizing a utility function related to the attractiveness of the path. Attractiveness depends on several features, such as a service facility, a restaurant serving typical food, an historical village, or a scenic landscape to be enjoyed along the way. Two kinds of resource constraints bound the solution. A path maximum duration, which depends on how many times each arc is traversed, and a maximum budget for setting up the infrastructure, which depends on which arcs are selected. Since a cyclist may be willing to traverse an edge more than once - think, for example, of a detour from the main way to be travelled back and forth to reach a point of interest – cycles can be part of the route. The attractiveness function is concave and decreases after reaching its maximum at a few traversals. Such features make the problem new and challenging. We present an integer linear programming model and validate it by an experimental campaign on realistic data for the Trebon region

Designing the master schedule for demand-adaptive transit systems

Abstract Demand-Adaptive Systems (DAS) display features of both traditional fixed-line bus services and purely on-demand systems such as dial-a-ride, that is they offer demand-responsive services within the framework of traditional scheduled bus transportation. A DAS bus line serves, on one hand, a given set of compulsory stops according to a predefined schedule specifying the time windows associated with each, providing the traditional use of the transit line, without requiring any reservation. On the other hand, passengers may also issue requests for transportation between two desired, optional, stops, which induces detours in the vehicle routes. The design of a DAS line is a complex planning operation that requires to determine not only its design in terms of selecting the compulsory stops, but also its master schedule in terms of the time windows associated with the compulsory stops. Designing a DAS thus combines elements of strategic and tactical planning. In this paper we focus on determining a master-schedule for a single DAS line. We propose a mathematical description and a solution framework based on the estimation of a number of statistical parameters of the demand and the DAS line service. Results of numerical experiments are also given and analyzed

The Gateway Location Problem: A Cost Oriented Analysis of a New Risk Mitigation Strategy in Hazmat Transportation

Modern societies rely upon massive supplies of large amounts of commodities, some of which imply the use of hazardous materials (hazmat). A crucial step in the hazmat life cycle is transportation. An accident en route is a “low probability - high consequences” event and much effort has been devoted to the development of risk mitigation strategies. In this paper we are concerned with hazmat transportation by truck on a road network, where several alternative itineraries from origin to destination are worthy of choice. Given a set of origin-destination pairs and the hazmat quantities to be transported for each pair, the road network topology, and the cost and the risk of each arc, the aim is to reduce the total risk related to the hazmat itineraries, hopefully not to a sensitive detriment of cost. In a mixed urban setting, the shortest path is often a risky one. Whenever possible, the network administrator imposes to each driver a specific itinerary with lower risk. If not possible, the network administrator may enforce some restrictions regarding network usage, such as forbidding hazmat transit on some links or imposing tolls. Within this framework, we propose a new method that diverts vehicles from their shortest (and risky) path from origin to destination, by forcing each vehicle to pass through an intermediate check point, so called gateway. We face the problem of selecting the location of a given number of gateways among a larger number of potential locations and assigning a gateway to each vehicle such that the total risk is minimized. Once gateways are located and assigned, the “rational” driver will travel along the shortest path from its origin to its assigned gateway, and then from such a gateway to its destination. While previous studies have experimentally demonstrated the efficacy of our strategy, the issue of the cost of the solutions has never been analyzed in depth. In this work we describe how to efficiently compute the Pareto frontier given by the non dominated solutions with respect to total risk and total cost on realistic instances taken from the literature, and we present computational results showing that the solution yielded by our method represents a very good compromise between the two criteria since it achieves substantial risk mitigation while providing an efficient trade off with cost

Routing hazardous materials by compulsory check points in case of variable demand

The Gateway Location Problem is the core of a new system for Hazardous Material routing, whose risk mitigation potentials have been assessed in case of static demand. We investigate the impact of flexibility in gateway location and allocation decisions in case of variable demand, and provide a tool to support decision makers in establishing a trade off between infrastructure costs and risk mitigation targets