#8873: Inconsistency with CombinatorialFreeModule: Vector Space vs. Module
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Reporter: jbandlow | Owner: robertwb
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Changes (by tscrim):
* cc: nthiery (added)
* owner: nthiery => robertwb
* component: categories => coercion
* milestone: sage-duplicate/invalid/wontfix => sage-6.4
Comment:
The problem actually stems from this:
{{{
sage: G(1) in ZZ
True
sage: G(1) in QQ
False
}}}
First off, I think this behavior is very inconsistent. Pertaining to this
ticket, I think this should be fixed as it was made explicit that we
wanted an element of the indexing set. The natural thing to do would be to
check the parent matches the indexing set provided the indices do not
coerce into the base ring (to avoid the ambiguity). Yet this has a subtly
with say you take `4 / 2`, this is now in `QQ`, and pass that to a CFM
with indices QQ and base ring ZZ and you might unexpectedly get `B[2]` as
opposed to `2*B[0]` (or whatever the one basis element is).
Although I guess for modules, there is no ambiguity; it's only for unital
algebras that such a conversion is (naturally) defined, right? So perhaps
we want to refactor things around and have separate behavior for non-
unital algebras.
Thoughts?
--
Ticket URL: <http://trac.sagemath.org/ticket/8873#comment:7>
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