There are a number of different techniques and criteria that can be used to decide how and when a net should be routed. Vertical constraint graphs and merging, used by “efficient algorithms for channel routing”, are two of these techniques, others include criteria such as congestion, wire length, minimal rectilinear Steiner tree, etc.. There are two steps in effective utilization of these criteria. The first step is the calculation of the criteria and the second step is their utilization. This chapter describes the first step, calculation of these criteria. Chapter 5 describes the second step, i.e. implementation of knowledge-based expert sources that adapt and utilize one or more of the calculations, described in this chapter, as their decision making criteria to achieve better routing and higher completion rates.
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