On Fri, 4 Feb 2022, 11:02 David Joyner, <wdjoy...@gmail.com> wrote: > On Fri, Feb 4, 2022 at 4:40 AM 'Michel VAN DEN BERGH' via sage-support > <sage-support@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+unsubscr...@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+unsubscr...@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/CAAWYfq0n7o-GWo9uNK5kQg2%2BQ63%2Bi3N8CAPJ6c%2B2S%2B7O2_fwJA%40mail.gmail.com.
