Thanks, Your reply was very helpful. Since I can also report that while using ...SmallGroup(IdGroup... calculation was measurably faster. In my case: calculations that took >> 10 minutes ( I don't know the actual time, I cancelled after 10 min) are now done in seconds.
Kind regards, nilo 2006/2/11, Jack Schmidt <[EMAIL PROTECTED]>: > Howdy, as a quick fix you convert the matrix group to a > representation that is easier for GAP to use: > > for i in [1..10] do > Print(i,": ", > StructureDescription(SmallGroup(IdGroup(testG(8,i)))), > "\n"); > od; > > This should print: > > 1: QD16 > 2: (C8 x C4) : C2 > 3: C3 x QD16 > 4: (C16 x C4) : C2 > 5: C5 x QD16 > 6: C3 x ((C8 x C4) : C2) > 7: C7 x QD16 > 8: (C32 x C4) : C2 > 9: C9 x QD16 > 10: C5 x ((C8 x C4) : C2) > > > The (silly) reason this works is because IdGroup is an older more > mature function which has been tested and fixed for many years to > handle all sorts of groups given to it. StructureDescription is > much newer and does not yet protect itself against hard questions. > > > > On Sat, February 11, 2006 07:56, Nilo de Roock wrote: > > Hello GAP forum, > > > > I have posted some questions regarding StructureDescription() > > recently, thank you for all answers. ( It came a bit as a shock to me > > but I now understand that non-isomorphic groups can have the same > > structure description. So yes the answers have been -very- helpful. I > > have also updated to the latest GAP releases, both kernel and > > packages. ) > > > > I am however still a bit uncertain about how I should interpret the > > answers of StructureDescription() and what is the best (simplest) > > method of finding the structure of a group. Let me give an example. > > > > <EXAMPLE> > > I am doing some experiments regarding generating sets of matrices and > > the structure of the group they generate. I use for example the > > following function: > > > > testG:=function(a,b) > > local M1; > > M1:=[[ [ 0, -E(a)^-1 ], [ -E(a), 0 ] ],[ [ 0, -1 ], [ 1, 0 ] ], [ [ > > E(4*b), 0 ], [ 0, -E(4*b) ] ],[ [ -1, 0 ], [ 0, -1 ] ]]; > > return (Group(M1)); > > end; > > > > I noticed the (for me...) interesting result that > > StructureDescription(testG(8,1)) = QD16 > > StructureDescription(testG(8,3)) =C3 X QD16 > > StructureDescription(testG(8,5))= C5 X QD16 > > For other numbers however... > > StructureDescription(testG(8,2))= GAP Error* > > StructureDescription(testG(8,4))= GAP Error* > > StructureDescription(testG(8,7))= GAP Error* > > > > *="... Error, no method found! For debugging hints type ?Recovery from > > NoMethodFound > > Error, no 2nd choice method found for `IsNaturalGL' on 1 arguments called > > fro\ > > m..." > > ( I interpreted the errors as "does not generate a group", or a bug in > > StructureDescription() for which a fix is due...) > > > > Size(testG(8,1))= 16 > > Size(testG(8,2))= 64 > > Size(testG(8,3))= 48 > > Size(testG(8,4))= 128 > > Size(testG(8,5))= 80 > > Size(testG(8,6))= 192 > > Size(testG(8,7))= 112 > > So there -are- groups generated. But which ones? > > > > ( Starting from Size(testG(4,7*11))= 176 computation time increased > > noticably. ) > > </EXAMPLE> > > > > In this particular example I would very much like to know which group > > is generated in testG(8,2). Can GAP give an answer to that? Will the > > forthcoming update in StructureDescription() address this issue(if an > > issue at all)? > > > > More in general, am I perhaps using StructureDescription() in a wrong > > way or am I expecting too much from the command? > > > > Thanks in advance for any advice. > > nilo > > > > _______________________________________________ > > Forum mailing list > > [email protected] > > http://mail.gap-system.org/mailman/listinfo/forum > > > > > _______________________________________________ Forum mailing list [email protected] http://mail.gap-system.org/mailman/listinfo/forum
