Dear Jack, Dear Steve, Thanks again for the helpful replies.
> > I'm too accustomed to programming in perl where I protect myself > > (most of the time) by "if defined ... then". > > > We are working on this. Already, many functions return 'fail' rather than > giving errors (for instance trying to invert a singular matrix) to allow these > conditions to be detected, but we are working on a general mechanism for > catching errors. Ok, I was not aware that there were so many differences in the programming (e.g., I noted about 1000 instances of 'fail') and had preseumed that the programs all followed, more or less, the same standards. > I'll leave your remaining question, about normal subgroups for someone else to > answer. No suggestions yet. I hope there is still the patience to answer a few more questions: If one wanted to write a function, SubLattice say, that might behave in some reasonable way, e.g., maybe something like l:=LatticeSubgroups(G); n:=SubLattice(l,x->NormalSubgroups(G)); where SubLattice is supposed to remove all nodes and edges from l except for those in the collection of subgroups given (at the moment I won't worry if the resulting structure is actually a lattice), one at least needs to understand the way the lattice structure is stored in l. How do I determine that? IsRecord, IsRecordCollection, IsRecordCollColl all returned false. Display doesn't help. Is there a list of 'types' of objects used in GAP? If so, I somehow missed it. [I guess the code in xgap might give some hints, but I haven't had a chance to look at that carefully yet.] And a related question, if for example, I wanted to determine how RankMat worked, say, I wondered if (and I'm sure it does) immediately returned n as the rank for an m x n matix for m > n once enough independent rows are found, how would I go about tracing backwards through the code to find this? I'm sure these sorts of things have been asked before & there's probably some place I should have already looked, but I didn't manage to find it. I hope I'm not being too much of a pain. Thanks again for all your help! Keith _______________________________________________ Forum mailing list [email protected] http://mail.gap-system.org/mailman/listinfo/forum
