#17859: Wrong coercion between QQ and finite rings
------------------------------+------------------------
Reporter: vdelecroix | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.6
Component: coercion | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Description changed by vdelecroix:
Old description:
> There is no coercion between QQ and finite rings
> {{{
> sage: cm = get_coercion_model()
> sage: cm.get_action(Zmod(2), QQ, operator.mul) is None
> True
> }}}
> This is right.
>
> But we do have an action of matrices on vectors
> {{{
> sage: M = MatrixSpace(Zmod(2),2)
> sage: V = VectorSpace(QQ,2)
> sage: cm.get_action(M,V,operator.mul)
> Left action by
> Full MatrixSpace of 2 by 2 dense matrices over Ring of integers modulo
> 2 on
> Vector space of dimension 2 over Rational Field
> }}}
> or
> {{{
> sage: M = MatrixSpace(QQ,2)
> sage: V = VectorSpace(Zmod(2),2)
> sage: cm.get_action(M,V,operator.mul)
> Left action by
> Full MatrixSpace of 2 by 2 dense matrices over Rational Field on
> Vector space of dimension 2 over Ring of integers modulo 2
> }}}
> And this is wrong!
New description:
There is no coercion between QQ and finite rings
{{{
sage: cm = get_coercion_model()
sage: cm.get_action(Zmod(2), QQ, operator.mul) is None
True
}}}
This is right.
But we do have an action of matrices on vectors
{{{
sage: M = MatrixSpace(Zmod(2),2)
sage: V = VectorSpace(QQ,2)
sage: cm.get_action(M,V,operator.mul)
Left action by
Full MatrixSpace of 2 by 2 dense matrices over Ring of integers modulo 2
on
Vector space of dimension 2 over Rational Field
}}}
or
{{{
sage: M = MatrixSpace(QQ,2)
sage: V = VectorSpace(Zmod(2),2)
sage: cm.get_action(M,V,operator.mul)
Left action by
Full MatrixSpace of 2 by 2 dense matrices over Rational Field on
Vector space of dimension 2 over Ring of integers modulo 2
}}}
And this is wrong!
see also: #12865
--
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Ticket URL: <http://trac.sagemath.org/ticket/17859#comment:1>
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