GroupSetwiseStabilizer

GroupSetwiseStabilizer[group,{p1,,pn}]

returns the subgroup of group for which the images of the points pi are still in the list {p1,,pn}.

GroupSetwiseStabilizer[group,{p1,,pn},f]

returns the setwise stabilizer subgroup under the action given by the function f.

Details

  • Group elements in the setwise stabilizer do not necessarily fix the points pi.
  • The pointwise stabilizer of a list of points, computed with GroupStabilizer, is a subgroup of the setwise stabilizer of the same list of points.
  • The output is a subgroup of group defined by generators, but possibly using different generators.
  • Evaluation of f[p,g] for an action function f, a point p and a permutation g of the given group, is assumed to return another point p'.
  • For permutation groups, the default group action is taken to be PermutationReplace.

Examples

open allclose all

Basic Examples  (1)

Setwise stabilizer of four points:

Take an element of the stabilizer:

It moves the points of the list among them:

Scope  (3)

Compute the setwise stabilizer of a permutation group defined by generators:

Possible results of the action of the elements of the setwise stabilizer:

Compute the setwise stabilizer of a named permutation group:

Possible results of the action of the elements of the setwise stabilizer:

Subgroup of permutations that leave invariant a set of lists of objects under Permute action:

Check that such a set does indeed form a single orbit under Permute action:

Properties & Relations  (2)

Take the group:

And the list of points to stabilize:

Compute the setwise stabilizer:

And the pointwise stabilizer:

Check that the pointwise stabilizer is a subgroup of the setwise stabilizer:

Compare the possible reorderings of the list in both cases. The six reorderings correspond to the six cosets of the stabilizer in the setwise stabilizer:

Subgroup of permutations that leave invariant a set of lists of objects under Permute action:

Check that such a set does indeed form a single orbit under Permute action:

Compare with the result of GroupStabilizer, giving a smaller subgroup:

Now each list of objects forms its own orbit:

Introduced in 2010
 (8.0)
 |
Updated in 2012
 (9.0)