On the existence of polynomial time approximation schemes for OBDD minimization (extended abstract)

Abstract

The size of Ordered Binary Decision Diagrams (OBDDs) is determined by the chosen variable ordering. A poor choice may cause an OBDD to be too large to fit into the available memory. The decision variant of the variable ordering problem is known to be NP-complete. We strengthen this result by showing that there is no polynomial time approximation scheme for the variable ordering problem unless P = NP. We also prove a small lower bound on the performance ratio of a polynomial time approximation algorithm under the assumption P ≠ NP. © 1998 Springer-Verlag.