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Free/Braid groups not working

asked 2018-11-02 12:05:55 +0100

danieleC gravatar image

updated 2019-09-16 13:47:25 +0100

FrédéricC gravatar image

Hi, I am working with SageMath 8.1, and it seems like "FreeGroup()" (and as a consequence BraidGroup() ) are not working properly. If I write in the notebook

G.<a,b,c> = FreeGroup()

I get the following:

Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "", line 10, in <module>
exec compile(u'open("","w").write("# -*- coding: utf-8 -*-\\n" + _support_.preparse_worksheet_cell(base64.b64decode("Ry48YSxiLGM+ID0gRnJlZUdyb3VwKCk="),globals())+"\\n"); execfile(os.path.abspath(""))
File "", line 1, in <module>

File "/tmp/tmpFDI_RE/", line 2, in <module>
exec compile(u"G = FreeGroup(names=('a', 'b', 'c',)); (a, b, c,) = G._first_ngens(3)" + '\n', '', 'single')
File "", line 1, in <module>

File "sage/misc/lazy_import.pyx", line 388, in sage.misc.lazy_import.LazyImport.__call__ (build/cythonized/sage/misc/lazy_import.c:4118)
File "/usr/lib/python2.7/dist-packages/sage/groups/", line 648, in FreeGroup
return FreeGroup_class(names)
 File "sage/misc/classcall_metaclass.pyx", line 330, in sage.misc.classcall_metaclass.ClasscallMetaclass.__call__ (build/cythonized/sage/misc/classcall_metaclass.c:1481)
 File "sage/misc/cachefunc.pyx", line 1059, in sage.misc.cachefunc.CachedFunction.__call__ (build/cythonized/sage/misc/cachefunc.c:6162)
  File "/usr/lib/python2.7/dist-packages/sage/structure/", line 1021, in __classcall__
instance = typecall(cls, *args, **options)
 File "sage/misc/classcall_metaclass.pyx", line 497, in sage.misc.classcall_metaclass.typecall (build/cythonized/sage/misc/classcall_metaclass.c:1931)
 File "/usr/lib/python2.7/dist-packages/sage/groups/", line 736, in __init__
libgap_free_group = libgap.FreeGroup(generator_names)
 File "sage/libs/gap/element.pyx", line 2213, in (build/cythonized/sage/libs/gap/element.c:17671)
ValueError: libGAP: Error, FreeGroup: function is not yet defined

Am I doing something wrong? Thanks!

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  • What operating system?

  • How was Sage installed?

    • via a package manager? (apt, brew, conda, nix, yum...)
    • platform-specific binaries downloaded from the SageMath website?
    • built from source?
slelievre gravatar imageslelievre ( 2018-11-02 12:55:58 +0100 )edit

Ubuntu 18.04, I am on a university machine, so I have no idea of how it was installed!

danieleC gravatar imagedanieleC ( 2018-11-02 14:42:22 +0100 )edit

Perhaps should you contact your university's system administrator.

tmonteil gravatar imagetmonteil ( 2018-11-02 15:34:42 +0100 )edit

You could try running in a terminal apt list --installed sagemath sagemath-jupyter to check if these packages were installed with apt.

slelievre gravatar imageslelievre ( 2018-11-03 00:57:53 +0100 )edit

Got `Listing... Done

sagemath/bionic,now 8.1-7ubuntu1 amd64 [installed]`"

danieleC gravatar imagedanieleC ( 2018-11-05 15:18:20 +0100 )edit

Any chance this could be solved easily? or should I just downgrade both ubuntu and sage?

danieleC gravatar imagedanieleC ( 2018-11-21 15:34:23 +0100 )edit

1 Answer

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answered 2018-11-22 12:24:40 +0100

slelievre gravatar image

If the disk space available to you on that machine allows it, I would suggest visiting the SageMath download page for Linux, selecting your favourite mirror (or use the torrent if you can), and downloading the binary distribution for Ubuntu 18.04, ie the file sage-8.4-Ubuntu_18.04-x86_64.tar.bz2.

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that worked!! thanks a lot!

danieleC gravatar imagedanieleC ( 2018-11-24 14:59:55 +0100 )edit

Or you could ask your system administrators to do that, if several users of these machines have an interest in using Sage.

slelievre gravatar imageslelievre ( 2018-11-24 15:50:47 +0100 )edit

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Asked: 2018-11-02 12:05:55 +0100

Seen: 182 times

Last updated: Nov 22 '18