Computing modular invariants of p-groups

  • Authors:
  • R. James Shank;David L. Wehlau

  • Affiliations:
  • Institute of Mathematics & Statistics, University of Kent at Canterbury, CT2 7NF, U.K.;Department of Mathematics & Computer Science, Royal Military College, Kingston, Ontario, Canada K7K 7B4

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2002

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Abstract

Let V be a finite dimensional representation of a p-group, G, over a field, k, of characteristic p. We show that there exists a choice of basis and monomial order for which the ring of invariants, k[V]G, has a finite SAGBI basis. We describe two algorithms for constructing a generating set for k[V]G. We use these methods to analyse k[2V3]U3 where U3 is the p-Sylow subgroup of GL3(Fp) and 2V3 is the sum of two copies of the canonical representation. We give a generating set for k[2V3]U3 for p = 3 and prove that the invariants fail to be Cohen-Macaulay for p 2. We also give a minimal generating set for k[mV2]Z/p were V2 is the two-dimensional indecomposable representation of the cyclic group Z/p.