Finding small OBDDs for incompletely specified truth tables is hard

  • Authors:
  • Jesper Torp Kristensen;Peter Bro Miltersen

  • Affiliations:
  • Department of Computer Science, University of Aarhus, Denmark;Department of Computer Science, University of Aarhus, Denmark

  • Venue:
  • COCOON'06 Proceedings of the 12th annual international conference on Computing and Combinatorics
  • Year:
  • 2006

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Abstract

We present an efficient reduction mapping undirected graphs G with n = 2k vertices for integers k to tables of partially specified Boolean functions g: {0,1}$^{\rm 4{\it k}+1}$ →{0,1,⊥} so that for any integer m, G has a vertex colouring using m colours if and only if g has a consistent ordered binary decision diagram with at most (2m + 2)n2 + 4n decision nodes. From this it follows that the problem of finding a minimum-sized consistent OBDD for an incompletely specified truth table is NP-hard and also hard to approximate.