Accelerating OBDD-Minimization by Means of Structural and Semantical Properties

Abstract

In many different applications in computer science, the representation of Boolean functions is done in terms of Ordered Binary Decision Diagrams (OBDD). This is particulary true in the field of computer aided design of VLSI circuits. Within the graph-based data structure of an OBDD the variable order may have a tremendeous impact on the size of the graph. An OBDD package is the core of diverse software systems for computer aided design and hence, its efficiency has a huge influence on the performance of these systems. Due to the impact of the chosen variable order on the OBDD-size as well memory as time requirements of such OBDD-packages depend strongly on how the problem of finding an optimal variable order is solved. Since this problem is known to be NP-hard, there is a need for efficient heuristics that find variable orderings in feasible time within an acceptable memory overhead. The most universal and successful approach for doing this is based on suited dynamical changes of the v..