ABSTRACT
This chapter examines force-directed methods by considering how some of the work and other continuous placement methods that, although not seemingly force-directed, share characteristics with force-directed methods. It describes the traditional force-directed method that employs quadratic optimization to minimize wirelength and additional constant forces to remove cell overlap. The chapter also describes methods that use techniques other than constant forces to eliminate cell overlap. It also describes several issues facing force-directed methods. Force-directed methods have been studied over the past four decades as a means of placing cells. The clique model results in a denser quadratic optimization problem, whereas the star model tends to improve the sparsity of the problem, but requires additional dummy cells to represent the star nodes. The future of force-directed methods is a promising area of research in the field of very large scale integrated computer-aided design.
