Free/Braid groups not working

asked 2018-11-02 06:05:55 -0600

danieleC 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 06:55:58 -0600 )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 08:42:22 -0600 )edit

Perhaps should you contact your university's system administrator.

tmonteil gravatar imagetmonteil ( 2018-11-02 09:34:42 -0600 )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 ( 2018-11-02 18:57:53 -0600 )edit

Got `Listing... Done

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

danieleC gravatar imagedanieleC ( 2018-11-05 08:18:20 -0600 )edit