[GAP Forum] Issue with finitely presented groups

[Paul Timmons]

Having downloaded Gap 4.9.3 I found there seems to be an issue with
computing orders of groups of greater than 1000 which were pretty immediate
in older versions. Is there some setting for coset size or other that needs
adding? e. g. the presentation for M22 in the Atlas. F:=FreeGroup("a",
"b");a:=F. 1;b:=F.2;rels:=<relators of the group>;G:=F/rels;Order(G) ;
<hangs>

[Max Horn]

Dear Paul,

Post by Paul Timmons
Having downloaded Gap 4.9.3 I found there seems to be an issue with
computing orders of groups of greater than 1000 which were pretty immediate
in older versions. Is there some setting for coset size or other that needs
adding? e. g. the presentation for M22 in the Atlas. F:=FreeGroup("a",
"b");a:=F. 1;b:=F.2;rels:=<relators of the group>;G:=F/rels;Order(G) ;
<hangs>

Thank you for your report. However, could you please be a bit more specific, and give us a concrete set of inputs that demonstrate the regression?

Regards,
Max

[Hulpke,Alexander]

Dear Forum, Dear Paul Timmons,

Having downloaded Gap 4.9.3 I found there seems to be an issue with
computing orders of groups of greater than 1000 which were pretty immediate
in older versions.
Thank you for the report.

I looked through the (rewritten because of a lack of maintainer of the previous version) code for the Modified Todd-Coxeter that is used in this calculations and discovered a problem that leads to severe performance degradation in larger examples. A fix is submitted for inclusion in a future release.

Regards,

Alexander Hulpke

-- Colorado State University, Department of Mathematics,
Weber Building, 1874 Campus Delivery, Fort Collins, CO 80523-1874, USA
email: ***@colostate.edu<mailto:***@colostate.edu>, http://www.math.colostate.edu/~hulpke




On Sep 12, 2018, at 2:24 PM, Paul Timmons <***@gmail.com<mailto:***@gmail.com>> wrote:

Having downloaded Gap 4.9.3 I found there seems to be an issue with
computing orders of groups of greater than 1000 which were pretty immediate
in older versions. Is there some setting for coset size or other that needs
adding? e. g. the presentation for M22 in the Atlas. F:=FreeGroup("a",
"b");a:=F. 1;b:=F.2;rels:=<relators of the group>;G:=F/rels;Order(G) ;
<hangs>