The nonapproximability of OBDD minimization

  • Authors:
  • Detlef Sieling

  • Affiliations:
  • Univ. Dortmund, Federal Republic of Germany

  • Venue:
  • Information and Computation
  • Year:
  • 2002

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Abstract

The size of ordered binary decision diagrams (OBDDs) is determinedby the chosen variable ordering. A poor choice may cause an OBDD tobe too large to fit into the available memory. The decision variantof the variable ordering problem is known to be NP-complete.We strengthen this result by showing that, unlessP=NP, for each constant c1 there is nopolynomial time approximation algorithm with the performance ratioc for the variable ordering problem, i.e., no polynomialtime algorithm that guarantees the computation of a variableordering so that the resulting OBDD size is larger than the minimumsize by a factor of at most c. This result justifies, alsofrom a theoretical point of view, the use of heuristics for thevariable ordering problem.