Derivation Tree Analysis for Accelerated Fixed-Point Computation

  • Authors:
  • Javier Esparza;Stefan Kiefer;Michael Luttenberger

  • Affiliations:
  • Institut für Informatik, Technische Universität München, Garching, Germany 85748;Institut für Informatik, Technische Universität München, Garching, Germany 85748;Institut für Informatik, Technische Universität München, Garching, Germany 85748

  • Venue:
  • DLT '08 Proceedings of the 12th international conference on Developments in Language Theory
  • Year:
  • 2008

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Abstract

We show that for several classes of idempotent semirings the least fixed-point of a polynomial system of equations is equal to the least fixed-point of a linearsystem obtained by "linearizing" the polynomials of in a certain way. Our proofs rely on derivation tree analysis, a proof principle that combines methods from algebra, calculus, and formal language theory, and was first used in [5] to show that Newton's method over commutative and idempotent semirings converges in a linear number of steps. Our results lead to efficient generic algorithms for computing the least fixed-point. We use these algorithms to derive several consequences, including an O(N3) algorithm for computing the throughput of a context-free grammar (obtained by speeding up the O(N4) algorithm of [2]), and a generalization of Courcelle's result stating that the downward-closed image of a context-free language is regular [3].