Polar varieties and computation of one point in each connected component of a smooth real algebraic set

  • Authors:
  • Mohab Safey El Din;Éric Schost

  • Affiliations:
  • Université Paris, Paris, France;École polytechnique, Palaiseau, France

  • Venue:
  • ISSAC '03 Proceedings of the 2003 international symposium on Symbolic and algebraic computation
  • Year:
  • 2003

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Abstract

Let f1, ldots, fs be polynomials in Q[X1, ..., Xn] that generate a radical ideal and let V be their complex zero-set. Suppose that V is smooth and equidimensional; then we show that computing suitable sections of the polar varieties associated to generic projections of V gives at least one point in each connected component of V ∩ Rn. We deduce an algorithm that extends that of Bank, Giusti, Heintz and Mbakop to non-compact situations. Its arithmetic complexity is polynomial in the complexity of evaluation of the input system, an intrinsic algebraic quantity and a combinatorial quantity.