Now it seems "subs" does work. I must have done something wrong. Sorry for the noise.
On Friday, February 4, 2022 at 3:55:19 PM UTC+1 dim...@gmail.com wrote: > > > On Fri, 4 Feb 2022, 11:02 David Joyner, <wdjo...@gmail.com> wrote: > >> On Fri, Feb 4, 2022 at 4:40 AM 'Michel VAN DEN BERGH' via sage-support >> <sage-s...@googlegroups.com> wrote: >> > >> > Dear all, >> > >> > I need to do something which I thought would be quite simple. I have >> free groups >> > F, G with generators x1,x2,x3,x4 and x,y respectively and I need to >> compute the image of an element under the homomorphism F-->G:x1->x, x2->y, >> x3->x, x4->y. >> > >> > I could not find anything in the manual about morphisms between free >> groups. I tried subs, but that does not work since the parents of the >> elements of F and G are (of course) different. >> > >> > The workaround I used is to work in the free group H with generators >> x1,x2,x3,x4,x,y and to use subs. However this is also inconvenient since I >> need the action of the braid group with 4 strands on F. It does not act on >> H because of the limitation "#strands=#generators". >> > >> > So this means I have to use only part of the braid group with 6 strands. >> > >> > In the end it all works but it is terribly hacky for some which seems >> to be a very clean thing to do. >> > >> > I would be grateful for any suggestions. >> >> Michel: >> >> One idea is to check out >> https://doc.sagemath.org/html/en/reference/groups/sage/groups/braid.html >> >> Another idea is to download braid-1.1.tar.gz, untar in the pkg >> subdirectory and type LoadPackage("braid"); >> > > > most, if not all, functionality of braid is nowadays in > https://gap-packages.github.io/MapClass/ > > (which is in our gap_packages) > > > FYI, the pkg subdir is inside sage-9*/local/share/gap >> You can find a pdf manual for the braid package at >> https://arxiv.org/abs/math/0304376 >> Currently, the link to braid-1.1.tar.gz at >> https://www.gap-system.org/Packages/undep.html >> is bad but I have a copy. Just email me privately. >> >> - David >> >> > Michel >> > >> > >> > -- >> > You received this message because you are subscribed to the Google >> Groups "sage-support" group. >> > To unsubscribe from this group and stop receiving emails from it, send >> an email to sage-support...@googlegroups.com. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/sage-support/f7d460d0-390b-455d-ae90-72b105e8e926n%40googlegroups.com >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "sage-support" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to sage-support...@googlegroups.com. >> > To view this discussion on the web visit >> https://groups.google.com/d/msgid/sage-support/CAEQuuAVmSsLxS%2Bi50JNUqrK%3DUm%3DquJaZ2ueNuedAVzr6xKSMzQ%40mail.gmail.com >> . >> > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-support/44926720-4e3c-4567-94a3-8e2e6ff90a4cn%40googlegroups.com.
