#8412: Trivial Center of Matrix Group
----------------------------+-----------------------------------------------
Reporter: iandrus | Owner: joyner
Type: defect | Status: new
Priority: major | Milestone:
Component: group_theory | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
----------------------------+-----------------------------------------------
When calculating the center of a group, GAP returns an empty list of
generators if the center is trivial. This however throws off the creation
of the MatrixGroup in Sage which checks to ensure that there is at least
one generator.
{{{
sage: a=Matrix(FiniteField(5),
....: [[2,0,0],
....: [0,3,0],
....: [0,0,1]])
sage:
sage: b=Matrix(FiniteField(5),
....: [[0,1,0],
....: [4,0,0],
....: [0,0,1]])
sage:
sage: c=Matrix(FiniteField(5),
....: [[1,0,0],
....: [0,1,0],
....: [0,1,1]])
sage:
sage: d=Matrix(FiniteField(5),
....: [[1,0,0],
....: [0,1,0],
....: [1,0,1]])
sage:
sage: G = MatrixGroup([a,b,c,d])
sage: G.center()
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
/Users/gvol/Desktop/Sage-4.3.1.rc1.app/Contents/Resources/sage/<ipython
console> in <module>()
/Users/gvol/Desktop/Sage-4.3.1.rc1.app/Contents/Resources/sage/local/lib/python2.6
/site-packages/sage/groups/matrix_gps/matrix_group.pyc in center(self)
733 F = self.field_of_definition()
734 from sage.groups.matrix_gps.matrix_group import
MatrixGroup
--> 735 self.__center = MatrixGroup([g._matrix_(F) for g in G])
736 return self.__center
737
/Users/gvol/Desktop/Sage-4.3.1.rc1.app/Contents/Resources/sage/local/lib/python2.6
/site-packages/sage/groups/matrix_gps/matrix_group.pyc in
MatrixGroup(gens)
156 """
157 if len(gens) == 0:
--> 158 raise ValueError, "gens must have positive length"
159 try:
160 R = gens[0].base_ring()
ValueError: gens must have positive length
}}}
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8412>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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