On uncertainty versus size in branching programs

  • Authors:
  • S. Jukna;S. Žák

  • Affiliations:
  • Universität Frankfurt, Institut für Informatik, D-60054 Frankfurt, Germany and Institute of Mathematics and Informatics, LT-2600 Vilnius, Lithuania;Institute of Computer Science, Academy of Science, 18200 Prague 8, Czech Republic

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2003

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Abstract

We propose an information-theoretic approach to proving lower bounds on the size of branching programs. The argument is based on Kraft type inequalities for the average amount of uncertainty about (or entropy of) a given input during the various stages of computation. The uncertainty is measured by the average depth of so-called 'splitting trees' for sets of inputs reaching particular nodes of the program.We first demonstrate the approach for read-once branching programs. Then, we introduce a strictly larger class of so-called 'balanced' branching programs and, using the suggested approach, prove that some explicit Boolean functions cannot be computed by balanced programs of polynomial size. These lower bounds are new since some explicit functions, which are known to be hard for most previously considered restricted classes of branching programs, can be easily computed by balanced branching programs of polynomial size.