Computing Invariant Subspaces of Matrix Groups

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Does anyone have a program written in Mathematica (or SAGE or GAP) that computes the invariant subspace lattice of a matrix group?

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I am posting a CW answer to remove this question from the unanswered queue. Thanks to @Derek Holt and @Jack Schmidt for the comments that I've converted to the answer

It depends a little on the matrix group. If the matrix group is the one element group over the 6x6 matrices over Z/11Z then the lattice has 3 billion subspaces. If the associated module is "square-free" then things are much nicer, and GAP can handle this without trouble. The GAP command for this is MTX.BasesSubmodules which is described in the Meataxe chapter. MTX.BasesMinimalSubmodules and MTX.BasesMaximalSubmodules are also useful if there are too many of them.