#18756: Use cython and coercion for CombinatorialFreeModule
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Reporter: SimonKing | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.8
Component: algebra | Resolution:
Keywords: CombinatorialFreeModule, | Merged in:
cython, coercion | Reviewers:
Authors: | Work issues:
Report Upstream: N/A | Commit:
Branch: | Stopgaps:
Dependencies: |
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Comment (by SimonKing):
Here is how `CombinatorialFreeModuleElement` fails to use the coercion
framework properly.
It uses the method `_acted_upon_` to implement multiplication by scalars,
and then does
{{{
# For backward compatibility
_lmul_ = _acted_upon_
_rmul_ = _acted_upon_
}}}
However, it is clearly the job of `_lmul_/_rmul_` to implement a scalar
multiplication---not just for backward compatibility! Moreover, in
`_lmul_/_rmul_` one can assume that the second argument comes from the
base ring---in the current implementation, this has to be explicitly
tested, simply since there is no such assumption for `_acted_upon_`.
And what is worst: Using `_acted_upon_` is one way to implement a general
action that goes BEYOND the action of the base ring. If one wants to
implement an action of, say, a path algebra on a free module over a path
algebra, then one would "of course" use `_acted_upon_`---but by the
current design, it would break scalar multiplication.
--
Ticket URL: <http://trac.sagemath.org/ticket/18756#comment:1>
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