Rational invariants of a group action. Construction and rewriting

  • Authors:
  • Evelyne Hubert;Irina A. Kogan

  • Affiliations:
  • Project CAFE, INRIA, 06902 Sophia Antipolis, France;Department of Mathematics, North Carolina State University, Raleigh, NC 27695-8205, USA

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2007

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Abstract

Geometric constructions applied to a rational action of an algebraic group lead to a new algorithm for computing rational invariants. A finite generating set of invariants appears as the coefficients of a reduced Grobner basis. The algorithm comes in two variants. In the first construction the ideal of the graph of the action is considered. In the second one the ideal of a cross-section is added to the ideal of the graph. Zero-dimensionality of the resulting ideal brings a computational advantage. In both cases, reduction with respect to the computed Grobner basis allows us to express any rational invariant in terms of the generators.