On Sat, Jun 28, 2008 at 11:00 AM, John Cremona <[EMAIL PROTECTED]> wrote:
>
> It seems that what Dan Bump's instructions did not specify is what
> properties the class assigned to ._combinatorial_class must have.
> And it needs something which PermutationGroupElement does not have.
>
> Does that help?
Okay. Maybe the best thing is to write a wrapper to GAP's GroupRing function.
>
> John
>
> 2008/6/28 David Joyner <[EMAIL PROTECTED]>:
>>
>> Hi:
>>
>> Since there are some interesting error-correcting codes based on group
>> algebras over a finite field,
>> I'm making a stab at implementing group rings for permutation groups.
>> Dan Bump (offlist) suggested
>> looking at the CombinatorialAlgebra class in
>> sage.combinat.combinatorial_algebra.py. The docstring there
>> says, in part,
>>
>> The CombinatorialAlgebra base class makes it easy to define and work
>> with new combinatorial algebras in Sage.
>> ...
>> The important things to define are ._combinatorial_class which specifies
>> the combinatorial class that indexes the basis elements, ._one which
>> specifies the identity element in the algebra, ._name which specifies
>> the name of the algebra, ._prefix which is the string put in front of
>> each basis element, and finally a _multiply or _multiply basis method
>> that defines the multiplication in the algebra.
>>
>> Baed on that, I'd like to input
>>
>> class PermutationGroupRing(CombinatorialAlgebra):
>> def __init__(self, R, G):
>> self.group = G
>> self._combinatorial_class = PermutationGroupElement
>> self._one = G.identity()
>> self._name = 'Group ring of %s'%str(G)
>> self._prefix = ''
>> CombinatorialAlgebra.__init__(self, R)
>> def _multiply_basis(self, a, b):
>> c = a*b
>> return c
>>
>> and have a command like
>>
>> sage: PermutationGroupRing(ZZ,G)
>>
>> return a group ring. Instead, I get the traceback error
>>
>> {{{
>> ---------------------------------------------------------------------------
>> AttributeError Traceback (most recent call last)
>>
>> /home/wdj/sagefiles/sage-3.0.3.rc0/<ipython console> in <module>()
>>
>> /home/wdj/.sage/temp/hera/7513/_home_wdj_sagefiles_codes_group_rings_sage_6.py
>> in __init__(self, R, G)
>> 27 self._name = 'Group ring of %s'%str(G)
>> 28 self._prefix = ''
>> ---> 29 CombinatorialAlgebra.__init__(self, R)
>> 30 def _multiply_basis(self, a, b):
>> 31 c = a*b
>>
>> /home/wdj/sagefiles/sage-3.0.3.rc0/local/lib/python2.5/site-packages/sage/combinat/combinatorial_algebra.py
>> in __init__(self, R, element_class)
>> 679 #Set the dimension
>> 680 try:
>> --> 681 self._dim = self._combinatorial_class.count()
>> 682 except (ValueError, NotImplementedError):
>> 683 self._dim = None
>>
>> AttributeError: type object
>> 'sage.groups.perm_gps.permgroup_element.Permutation' has no attribute
>> 'count'
>> }}}
>>
>> which I can't decipher.
>>
>> Can anyone explain "AttributeError: type object
>> 'sage.groups.perm_gps.permgroup_element.Permutation' has no attribute
>> 'count'"
>> (in words of two syllables or less, if possible:-)?
>>
>> - David Joyner
>>
>> >
>>
>
> >
>
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