Relaxation and clustering in a local search framework: application to linear placement

This paper presents two primary results relevant to physical design problems in CAD/VLSI through a case study of the linear placement problem. First a local search mechanism which incorporates a neighborhood operator based on constraint relaxation is proposed. The strategy exhibits many of the desirable features of analytical placement while retaining the flexibility and non-determinism of local search. The second and orthogonal contribution is in netlist clustering. We characterize local optima in the linear placement problem through a simple visualization tool-the displacement graph. This characterization reveals the relationship between clusters and local optima and motivates a dynamic clustering scheme designed specifically for escaping such local optima. Promising experimental results are reported