Dear Alexander, Thank you for your insights! Indeed, SubgroupProperty sped things up, and everything works fast now.
There was a little issue when the returned subgroup is trivial, it caused error in my subsequent code, but I can easily treat this case separately. (I posted it in github.) Best, Ignat https://www.math.lsu.edu/~ignatsoroko/ On Mon, Aug 3, 2020 at 10:51 AM Hulpke,Alexander < alexander.hul...@colostate.edu> wrote: > Dear Forum, Dear Ignat Soroko, > > > Is there a way to make GAP > > pass to a smaller generating set? Unfortunately, commands like > > SmallGeneratingSet(Aut); never terminate. > > If you have a group with 10^5 generators or so probably a lot of the > standard routines will reduce to a crawl -- e.g. `SmallGeneratingSet` uses > the existing generator number as a starting point for reduction. > > However in your code you don't really need to collect all elements. Do the > following changes > > > > G:=Group(Union(List(gen,x->GeneratorsOfGroup(SymmetricGroup(x))))); > > aut:=[]; > Aut:=Group(()); # trivial perm group > > for g in G do > > if ForAll([1..n-1],i->ForAll([i+1..n],j->m[i^g][j^g]=m[i][j])=true) then > > Add(aut,g); > Aut:=ClosureGroup(Aut,g); > > fi; > > od; > > This will eliminate redundant elements on the fly and result in a much > smaller generating set. > > even better would be to use existing information to avoid unneeded tests > (e.g. is you have already a subgroup U satisfying the condition and g does > not, no element in the coset Ug will do either). You can replace the whole > loop by: > > > Aut:=SubgroupProperty(G,g->ForAll([1..n-1],i->ForAll([i+1..n],j->m[i^g][j^g]=m[i][j])=true)); > > This is likely much faster. > > All the best, > > Alexander Hulpke > > > > _______________________________________________ Forum mailing list Forum@gap-system.org https://mail.gap-system.org/mailman/listinfo/forum
