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Abstract:

We consider the problem of isolating the real roots of a square-free polynomial with integer coefficients using (variants of) the continued fraction algorithm (CF). We introduce a novel way to compute a lower bound on the positive real roots of univariate polynomials. This allows us to derive a worst case bound of $\sOB(d^6 + d^4\tau^2 + d^3\tau^2)$ 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 $\tau$ the maximum bitsize of its coefficients. This improves the previous bound by Sharma \citesharma-tcs-2008 by a factor of $d^3$ and matches the bound derived by Mehlhorn and Ray \citemr-jsc-2009 for another variant of CF; it also matches the worst case bound of the subdivision-based solvers.

BibTeX:
@InProceedings{t-macis-icf-11,
  title =        {{Improved complexity bounds for real root isolation
                  using Continued Fractions}},
  author =       {Elias~P. Tsigaridas},
  booktitle =    "Proc. 4th Int'l Conf. on Mathematical Aspects of
                  Computer Information Sciences (MACIS)",
  year =         2011,
  address =      {Beijing, China},
  month =        {Oct},
  editor =       " S. Ratschan",
  pages =        "226--237",
  url =          {http://arxiv.org/abs/1010.2006},
  abstract =     "We consider the problem of isolating the real roots
                  of a square-free polynomial with integer
                  coefficients using (variants of) the continued
                  fraction algorithm (CF). We introduce a novel way to
                  compute a lower bound on the positive real roots of
                  univariate polynomials. This allows us to derive a
                  worst case bound of $\sOB(d^6 + d^4\tau^2 +
                  d^3\tau^2)$ 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 $\tau$ the maximum bitsize of its
                  coefficients. This improves the previous bound by
                  Sharma \cite{sharma-tcs-2008} by a factor of $d^3$
                  and matches the bound derived by Mehlhorn and Ray
                  \cite{mr-jsc-2009} for another variant of CF; it
                  also matches the worst case bound of the
                  subdivision-based solvers.",
}

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