Iterated discriminants

  • Authors:
  • Daniel Lazard;Scott McCallum

  • Affiliations:
  • UPMC Univ Paris 06, LIP6, F-75005, Paris, France and INRIA Paris-Rocquencourt, SALSA Project Team, F-78153 Le Chesnay, France and CNRS, LIP6, F-75005, Paris, France;Department of Computing, Division of ICS, Macquarie University, NSW 2109, Australia

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2009

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Abstract

It is shown that the discriminant of the discriminant of a multivariate polynomial has the same irreducible factors as the product of seven polynomials each of which is defined as the GCD of the generators of an elimination ideal. Under relatively mild conditions of genericity, three of these polynomials are irreducible and generate the corresponding elimination ideals, while the other four are equal to one. Moreover the irreducible factors of two of these polynomials have multiplicity at least two in the iterated discriminant and the irreducible factors of two others of the seven polynomials have multiplicity at least three. The proof involves an extended use of the notion of generic point of an algebraic variety and a careful study of the singularities of the hypersurface defined by a discriminant, which may be interesting by themselves.