Revisiting constraint-directed search

Revisiting constraint-directed search

We revisit the exploration of constraint-directed neighbourhoods, where a (small) set of constraints is picked before considering the neighbouring configurations where those constraints have a decreased (or preserved, or increased) penalty. Given the semantics of a constraint, such neighbourhoods can be represented via new attributes or primitives for the corresponding constraint object. We sho...

Constraint Directed Variable Neighbourhood Search

Local search algorithms operate by making small changes to candidate solutions with the aim of reaching new and improved solutions. The problem is that often the search will become trapped at sub optimal states from where there are no improving neighbours. Much research has gone into creating schemes to avoid these local optima and various strategies exist mainly based around altering the accep...

Constraint-directed search : a case study of job-shop scheduling

This thesis investigates the problem of constraint-directed reasoning in the job-shop scheduling domain. The job-shop scheduling problem is defined as: selecting a sequence of operations whose execution results in the completion of an order, and assigning times (i.e., start and end times) and resources to each operation. The number of possible schedules grows exponentially with the number of or...

A Constraint-directed Local Search Approach to Nurse Rostering Problems

In this paper, we investigate the hybridization of constraint programming and local search techniques within a large neighbourhood search scheme for solving highly constrained nurse rostering problems. As identified by the research, a crucial part of the large neighbourhood search is the selection of the fragment (neighbourhood, i.e. the set of variables), to be relaxed and re-optimized iterati...

Constraint-Directed Search: A Case Study of Job-Shop Scheduling