Bounding the radii of balls meeting every connected component of semi-algebraic sets

  • Authors:
  • Saugata Basu;Marie-Françoise Roy

  • Affiliations:
  • Department of Mathematics, Purdue University, West Lafayette, IN 47907, USA;IRMAR (URA CNRS 305), Université de Rennes 1, Campus de Beaulieu, 35042 Rennes, Cedex, France

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2010

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Abstract

We prove an explicit bound on the radius of a ball centered at the origin which is guaranteed to contain all bounded connected components of a semi-algebraic set S@?R^k defined by a weak sign condition involving s polynomials in Z[X"1,...,X"k] having degrees at most d, and whose coefficients have bitsizes at most @t. Our bound is an explicit function of s,d,k and @t, and does not contain any undetermined constants. We also prove a similar bound on the radius of a ball guaranteed to intersect every connected component of S (including the unbounded components). While asymptotic bounds of the form 2^@t^d^^^O^^^(^^^k^^^) on these quantities were known before, some applications require bounds which are explicit and which hold for all values of s,d,k and @t. The bounds proved in this paper are of this nature.