More on Noncommutative Polynomial Identity Testing

  • Authors:
  • Andrej Bogdanov;Hoeteck Wee

  • Affiliations:
  • University of California at Berkeley;University of California at Berkeley

  • Venue:
  • CCC '05 Proceedings of the 20th Annual IEEE Conference on Computational Complexity
  • Year:
  • 2005

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Abstract

We continue the study of noncommutative polynomial identity testing initiated by Raz and Shpilka and presentefficient algorithms for the following problems in the noncommutative model: Polynomial identity testing: The algorithm gets as an input an arithmetic circuit with the promise that the polynomial it computes has small degree (for instance, a circuit of logarithmic depth or an arithmetic formula) and determines whether or not the output of the circuit is identically zero (as a formal expression). Unlike the algorithm by Raz and Shpilka, our algorithm is black-box (but randomized with one-sided error) and evaluates the circuit over the ring of matrices. In addition, we present query complexity lower bounds for identity testing and explore the possibility of de-randomizing our algorithm. The analysis of our algorithm uses a noncommutative variant of the Schwartz-Zippel test. Minimizing algebraic branching programs: The algorithm gets as an input an algebraic branching program (ABP) and outputs a smallest equivalent ABP. The algorithm is based on Nisanýs characterization of ABP complexity, and uses as a sub-routine an algorithm for computing linear dependencies amongst arithmetic formulas, a problem previously studied by the authors.