Ideal decompositions and computation of tensor normal forms
<|reference_start|>Ideal decompositions and computation of tensor normal forms: Symmetry properties of r-times covariant tensors T can be described by certain linear subspaces W of the group ring K[S_r] of a symmetric group S_r. If for a class of tensors T such a W is known, the elements of the orthogonal subspace W^{\bot} of W within the dual space of K[S_r] yield linear identities needed for a treatment of the term combination problem for the coordinates of the T. We give the structure of these W for every situation which appears in symbolic tensor calculations by computer. Characterizing idempotents of such W can be determined by means of an ideal decomposition algorithm which works in every semisimple ring up to an isomorphism. Furthermore, we use tools such as the Littlewood-Richardson rule, plethysms and discrete Fourier transforms for S_r to increase the efficience of calculations. All described methods were implemented in a Mathematica package called PERMS.<|reference_end|>
@article{fiedler2002ideal,
    title={Ideal decompositions and computation of tensor normal forms},
    author={B. Fiedler},
    journal={Seminaire Lotharingien de Combinatoire, 45 (2001) Article B45g.
  http://www.mat.univie.ac.at/~slc/wpapers/s45fiedler.html},
    year={2002},
    archivePrefix={arXiv},
    eprint={math/0211156},
    primaryClass={math.CO cs.SC math.DG}
}