[GAP Forum] DirectFactorsOfGroup

[Bob Heffernan]

Dear all,

I want to check whether a group is indecomposable (i.e. it cannot be written as a direct product of smaller groups).  I'm making use of the GAP function DirectFactorsOfGroup, so a group is indecomposable if the list returned by this function has length 1.

This function is, however, undocumented.  My understanding is that it exists to be used by StructureDescription.  The documentation for StructureDescription mentions that it is primarily intended for small groups (of order less than 100) and I know it is intended as an educational tool more than anything else.

So, it is possibly the case that DirectFactorsOfGroup is intended only to be "good enough" for the purposes of StructureDescription and it might be that I shouldn't trust it too far.

The groups I'm looking at are all in the library of small groups, so they are "small" in that sense, but have orders larger than 100.

Can anybody shed any light on this?

Thank you & best regards,
Bob Heffernan