Complexity of real root isolation using continued fractions

  • Authors:
  • Vikram Sharma

  • Affiliations:
  • Max-Planck Institut für Informatik, Saarbrücken, 66123, Germany

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2008

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Abstract

In this paper, we provide polynomial bounds on the worst case bit-complexity of two formulations of the continued fraction algorithm. In particular, for a square-free integer polynomial of degree n with coefficients of bit-length L, we show that the bit-complexity of Akritas' formulation is O@?(n^8L^3), and the bit-complexity of a formulation by Akritas and Strzebonski is O@?(n^7L^2); here O@? indicates that we are omitting logarithmic factors. The analyses use a bound by Hong to compute the floor of the smallest positive root of a polynomial, which is a crucial step in the continued fraction algorithm. We also propose a modification of the latter formulation that achieves a bit-complexity of O@?(n^5L^2).