Complexity of real root isolation using continued fractions

  • Authors:
  • Vikram Sharma

  • Affiliations:
  • INRIA Sophia-Antipolis, France and NYU, USA

  • Venue:
  • Proceedings of the 2007 international symposium on Symbolic and algebraic computation
  • Year:
  • 2007

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Abstract

The efficiency of the continued fraction algorithm for isolating the real roots of a univariate polynomial depends upon computing tight lower bounds on the smallest positive root of a polynomial. The known complexity bounds for the algorithm rely on the impractical assumption that it is possible to efficiently compute the floor of the smallest positive root of a polynomial; without this assumption, the worst case bounds are exponential. In this paper, we derive the first polynomial worst case bound on the algorithm: for a square-free integer polynomial of degree n and coefficients of bit-length L, the bit-complexity of the continued fraction algorithm is Õ(n7L2),using a bound by Hong to compute the floor of the smallest positive root of a polynomial; here Õ indicates that we are omitting logarithmic factors.