Rational univariate representations of bivariate systems and applications

  • Authors:
  • Yacine Bouzidi;Sylvain Lazard;Marc Pouget;Fabrice Rouillier

  • Affiliations:
  • INRIA, Nancy, France;INRIA, Nancy, France;INRIA, Nancy, France;INRIA, Paris, France

  • Venue:
  • Proceedings of the 38th international symposium on International symposium on symbolic and algebraic computation
  • Year:
  • 2013

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Abstract

We address the problem of solving systems of two bivariate polynomials of total degree at most d with integer coefficients of maximum bitsize τ We suppose known a linear separating form (that is a linear combination of the variables that takes different values at distinct solutions of the system) and focus on the computation of a Rational Univariate Representation (RUR). We present an algorithm for computing a RUR with worst-case bit complexity in ÕB(d7+d6τ) and bound the bitsize of its coefficients by Õ(d2+dτ) (where ÕB refers to bit complexities and Õ to complexities where polylogarithmic factors are omitted). We show in addition that isolating boxes of the solutions of the system can be computed from the RUR with ÕB(d8+d7τ) bit operations. Finally, we show how a RUR can be used to evaluate the sign of a bivariate polynomial (of degree at most d and bitsize at most τ) at one real solution of the system in ÕB(d8+d7τ) bit operations and at all the ϴ(d2) solutions in only O(d) times that for one solution.