Abstract. We present a specialised binary constraint for the stable marriage problem. This constraint acts between a pair of integer variables where the domains of those variables represent preferences. Our constraint enforces stability and disallows bigamy. For a stable marriage instance with n men and women we require n 2 of these constraints, and the complexity of enforcing arc-consistency is O(n 3). Although this is non-optimal, empirical evidence suggests that in practical terms our encoding significantly outperforms the optimal encoding given in [7] in both space and time. 1

An instance I of the Hospitals / Residents problem (HR) involves a set of residents (graduating medical students) and a set of hospitals, where each hospital has a given capacity. The residents have preferences for the hospitals, as do hospitals for residents. A solution of I is a stable matching, which is an assignment of residents to hospitals that respects the capacity conditions and preference lists in a precise way. In this paper we present constraint encodings for HR that give rise to important structural properties. We also present a computational study using both randomly-generated and real-world instances. Our study suggests that Constraint Programming is indeed an applicable technology for solving this problem, in terms of both theory and practice. 1

Symmetry in a Constraint Satisfaction Problem can cause wasted search, which can be avoided by adding constraints to the CSP to exclude symmetric assignments or by modifying the search algorithm so that search never visits assignments symmetric to those already considered. One such approach is SBDS (Symmetry Breaking During Search); a modification is GAP-SBDS, which works with the symmetry group rather than individual symmetries. There has been little experience of how these techniques compare in practice. We compare their performance in finding all graceful labellings of graphs with symmetry. For these problems, GAP-SBDS is faster than SBDS unless there are few symmetries. When simple symmetry-breaking constraints can be found to break all the symmetry, GAP-SBDS is slower; if the constraints break only part of the symmetry, GAP-SBDS does less search and is faster. Eliminating symmetry has allowed us to find all graceful labellings, or prove that there are none, for several graphs whose gracefulness was not previously known. 1

Abstract. The stable marriage problem (SM) and the Hospital / Residents problem (HR) are both stable matching problems. They consist of two sets of objects that need to be matched to each other; in SM men to women, and in HR residents to hospitals. Each set of objects expresses a ranked preference for the objects in the other set, in the form of a preference list. The problem is then to find a matching of one set to the other such that matching is stable. We discuss issues concerning the creation of specialised constraints to solve these problems. We then present results that suggest that constraint programming is indeed a practical technology for solving these problems. 1

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The design of the AMPL modeling language stresses naturalness of expressions, generality of iterating over sets, separation of model and data, ease of data manipulation, and automatic updating of derived values when fundamental values change. We show how such principles have guided the addition of database access, complementarity modeling, and other language features.

Computer science has served to insulate programs and programmers from knowledge of the underlying mechanisms used to manipulate information, however this fiction is increasingly hard to maintain as computing devices decrease in size and systems increase in complexity. Manifestations of these limits appearing in computers include scaling issues in interconnect, dissipation, and coding. Reconfigurable Asynchronous Logic Automata (RALA) is an alternative formulation of computation that seeks to align logical and physical descriptions by exposing rather than hiding this underlying reality. Instead of physical units being represented in computer programs only as abstract symbols, RALA is based on a lattice of cells that asynchronously pass state tokens corresponding to physical resources. We introduce the design of RALA, review its relationships to its many progenitors, and discuss its benefits,

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Olsson.L. 2004. Optimisation of forest road investments and the roundwood supply chain.

Abstract In this paper, we present new results concerning the heuristic optimization of cable routing in electrical panels. The problem is modeled and a heuristic solution, using an insertion algorithm and a modified version of the Dijkstra’s algorithm, is proposed, analyzed, and compared with human-made solutions. Tests have shown that good results can be obtained from layouts commonly found in the industry.