Clustering and scheduling maintenance tasks over time

We report results on a maintenance scheduling problem. The problem consists of allocating maintenance task instances to and scheduling the performances of a suitable number of maintenance packages. The number of maintenance packages is not fixed, nor is, in general, the dates or durations of their performances. A constraint programming (CP) model and solver for the problem is presented together with preliminary computational results

MILP formulations of cumulative constraints for railway scheduling - A comparative study

This paper introduces two Mixed Integer Linear Programming (MILP) models for railway traffic planning using a cumulative scheduling constraint and associated pre-processing filters. We compare standard solver performance for these models on three sets of problems from the railway domain and for two of them, where tasks have unitary resource consumption, we also compare them with two more conventional models. In the experiments, the solver performance of one of the cumulative models is clearly the best and is also shown to scale very well for a large scale practical railway scheduling problem

Mixed integer-linear formulations of cumulative scheduling constraints - A comparative study

This paper introduces two MILP models for the cumulative scheduling constraint and associated pre-processing filters. We compare standard solver performance for these models on three sets of problems and for two of them, where tasks have unitary resource consumption, we also compare them with two models based on a geometric placement constraint. In the experiments, the solver performance of one of the cumulative models, is clearly the best and is also shown to scale very well for a large scale industrial transportation scheduling problem

Autonomous Accident Monitoring Using Cellular Network Data

Mobile communication networks constitute large-scale sensor networks that generate huge amounts of data that can be refined into collective mobility patterns. In this paper we propose a method for using these patterns to autonomously monitor and detect accidents and other critical events. The approach is to identify a measure that is approximately time-invariant on short time-scales under regular conditions, estimate the short and long-term dynamics of this measure using Bayesian inference, and identify sudden shifts in mobility patterns by monitoring the divergence between the short and long-term estimates. By estimating long-term dynamics, the method is also able to adapt to long-term trends in data. As a proof-of-concept, we apply this approach in a vehicular traffic scenario, where we demonstrate that the method can detect traffic accidents and distinguish these from regular events, such as traffic congestions

The Maraca: a tool for minimizing resource conflicts in a non-periodic railway timetable

While mathematical optimization and operations research receive growing attention in the railway sector, computerized timetabling tools that actually make significant use of optimization remain relatively rare. SICS has developed a prototype tool for non-periodic timetabling that minimizes resource conflicts, enabling the user to focus on the strategic decisions. The prototype is called the Maraca and has been used and evaluated during the railway timetabling construction phase at the Swedish Transport Administration between April and September 2010

A constraint model for a cyclic time personnel routing and scheduling problem

We present a crew scheduling problem with time windows in the context of scheduling train personnel, which encompasses not only assignment of resources to tasks but also the introduction of extra tasks, passive journeys, depending on the problem instance. The representation of the problem is made as a constraint program, which relies heavily on some global constraints, notably a constraint for expressing non-overlap between rectangles on a surface. A search algorithm is described and we also point out some problems and deficiencies of the current model and its computational behaviour

EWAM: An extension of WAM to execute functional programs

This paper describes a procedure for unification in extensional higher order logics. The procedure is due to Gerard Huet and was described in . In this paper we consider unification in extensional theories, which is a significantly simpler problem and is not described in detail in Huet's paper. In addition, the description here focuses on computation of substitutions rather than deciding unifiability, as in Huet's paper. To this some explanatory and clarifying material has been added

Task Structure Abstraction

This paper explores the idea of using formalised abstraction as means of describing various operations on structured representations of planing, scheduling and resource allocation problems. We define a notion of structures on tasks, relations and resources. Each task consists of task parameters and an inductively defined substructure. The task parameters denote domain variables constrained by the relations of the structure while resources formalises resource constraints, typically presupposing the semantics of some global constraint. A notion of consistency of such structures is briefly outlined. We go on characterise properties of safeness and certain conservation properties on operations We claim that such properties are relevant to problem domains where tasks on several different types or levels of resources has to scheduled simultaneously or by partitioning the problem into several subproblems that has then to be coordinated. Finally we present, in some detail, a model of such a problem from the rail transport industry formalised as several task structures. We show how operations on these can be seen as solvers for the various subproblems but also used to transform a specification or a solution of one subproblem into a specification of an other one. We claim that properties of such operations can be used to characterise reasoning in coordination problems

An approach to handling polymorphic types in higher order unification

The higher order unification procedure as formulated by Huet [Hu 75] unifies terms in the simple theory of types [Ch 40]. In this language types are expressed in a very weak language (no quantification, "->" being the only operator). In many applications a stronger type-system is desirable. Lambda Prolog [MN 86], e.g. uses a type system that is in some ways similar to that of ML. This type-system uses implicitly universally quantified variables in the type-expressions. It is not trivial to reformulate the higher order unification procedure for such a theory. This paper describes an implementation of the procedure that tries to overcome some of the problems encountered in such an endeavor. The basic approach taken is to let the types be an integral part of the representation of the terms to be unified. This makes it simpler to instanciate type-variables during the unification process, and to delay the unification of terms with completely unspecified types until such time as more information is gained

A higher order logic parser for natural language implemented in Lambda Prolog

This paper describes an implementation of some of the ideas presented by F.C.N. Pereira in [1]. Pereira uses a sequent-calculus like system to produce Montague semantics from natural language. The lefthand sequent can be interpreted as a set of constraints under which a given sentence fragment has a certain interpretation. Pereira presents a few complementary "discharge-rules" to reduce the number of such constraints. These conditional interpretations constitute a uniform way to represent partial knowledge during the parsing process. The implementation this paper describes is done in Lambda Prolog [2]. Lambda Prolog is a generalization of horn-clause logic to higher order logic, based on the higher order unification procedure of Huet [3]. It appears that the implementation of Pereira's system in Lambda Prolog becomes very natural. The higher order unification mechanism of Lambda takes care of the complicated binding mechanisms in Pereira's "discharge-rules" in a very simple and elegant way. Finally, the paper discusses some problems with the implementation and gives a few suggestions on how these could be overcome