Improved bounds for the CF algorithm

  • Authors:
  • Elias P. Tsigaridas

  • Affiliations:
  • -

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2013

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Abstract

We consider the problem of isolating the real roots of a square-free polynomial with integer coefficients using the classic variant of the continued fraction algorithm (CF), introduced by Akritas. We compute a lower bound on the positive real roots of univariate polynomials using an exponential search. This allows us to derive a worst-case bound of O@?"B(d^4@t^2) for isolating the real roots of a polynomial with integer coefficients using the classic variant of CF, where d is the degree of the polynomial and @t the maximum bitsize of its coefficients. This improves the previous bound of Sharma by a factor of d^3 and matches the bound derived by Mehlhorn and Ray for another variant of CF which is combined with subdivision; it also matches the worst-case bound of the classical subdivision-based solvers sturm, descartes, and bernstein.