Computing minimal multi-homogeneous bézout numbers is hard

  • Authors:
  • Gregorio Malajovich;Klaus Meer

  • Affiliations:
  • Departamento de Matemática Aplicada, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil;Department of Mathematics and Computer Science, University of Southern Denmark, Odense M, Denmark

  • Venue:
  • STACS'05 Proceedings of the 22nd annual conference on Theoretical Aspects of Computer Science
  • Year:
  • 2005

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Abstract

Computing good estimates for the number of solutions of a polynomial system is of great importance in many areas such as computational geometry, algebraic geometry, mechanical engineering, to mention a few. One prominent and frequently used example of such a bound is the multi-homogeneous Bézout number. It provides a bound for the number of solutions of a system of multi-homogeneous polynomial equations, in a suitable product of projective spaces. Given an arbitrary, not necessarily multi-homogeneous system, one can ask for the optimal multi-homogenization that would minimize the Bézout number. In this paper, it is proved that the problem of computing, or even estimating the optimal multi-homogeneous Bézout number is NP-hard. In terms of approximation theory for combinatorial optimization, the problem of computing the best multi-homogeneous structure does not belong to APX, unless P = NP. As a consequence, polynomial time algorithms for estimating the minimal multi-homogeneous Bézout number up to a fixed factor cannot exist even in a randomized setting, unless BPP⊒NP.