#4383: composition_series() returns no generators for trivial subgroup
--------------------------+-------------------------------------------------
Reporter: rbeezer | Owner: somebody
Type: defect | Status: new
Priority: minor | Milestone: sage-3.2.1
Component: group_theory | Keywords: composition series, generators
--------------------------+-------------------------------------------------
At the tail end of a composition series of a group, the trivial subgroup
has no generators, rather than the identity permutation as a generator.
This appears unacceptable to GAP for subsequent computations.
On 3.1.4 built from source on x86.
{{{
sage: G=CyclicPermutationGroup(2)
sage: comps
}}}
{{{
[Permutation Group with generators [(1,2)],
Permutation Group with generators []]
}}}
{{{
sage: comps[1].order()
}}}
{{{
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/rob/.sage/sage_notebook/worksheets/admin/48/code/5.py", line
7, in <module>
comps[_sage_const_1 ].order()
File "/opt/sage-3.1.4/local/lib/python2.5/site-
packages/SQLAlchemy-0.4.6-py2.5.egg/", line 1, in <module>
File "/opt/sage-3.1.4/local/lib/python2.5/site-
packages/sage/groups/perm_gps/permgroup.py", line 770, in order
return Integer(self._gap_().Size())
File "sage_object.pyx", line 270, in
sage.structure.sage_object.SageObject._gap_
(sage/structure/sage_object.c:2442)
File "sage_object.pyx", line 246, in
sage.structure.sage_object.SageObject._interface_
(sage/structure/sage_object.c:2186)
File "/opt/sage-3.1.4/local/lib/python2.5/site-
packages/sage/interfaces/expect.py", line 965, in __call__
return cls(self, x, name=name)
File "/opt/sage-3.1.4/local/lib/python2.5/site-
packages/sage/interfaces/expect.py", line 1283, in __init__
raise TypeError, x
TypeError: Gap produced error output
Error, usage: Group(<gen>,...), Group(<gens>), Group(<gens>,<id>)
executing $sage6:=Group([]);;
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/4383>
Sage <http://sagemath.org/>
Sage - Open Source Mathematical Software: Building the Car Instead of
Reinventing the Wheel
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