IsAbsolutelyIrreducible( module )
The G-module module is tested for absolute irreducibility, and true
or false is returned. If the result is false, then the dimension e
of the centralising field of module can be accessed by
DegreeFieldExtFlag(module). A matrix which centralises module
(that is, it centralises the generating matrices
GeneratorsFlag(module)) and which has minimal polynomial of degree
e over the ground field can be accessed as CentMatFlag(module). If
such a matrix is required with multiplicative order q^e-1, where q is
the order of the ground field, then FieldGenCentMat (see
FieldGenCentMat) can be called.
The algorithm is described in [5].
GAP 3.4.4