#11199: QuotientRing elements are not callable
-----------------------------+----------------------------------------------
Reporter: vbraun | Owner: AlexGhitza
Type: enhancement | Status: needs_info
Priority: major | Milestone: sage-4.7.1
Component: algebra | Keywords:
Work_issues: | Upstream: N/A
Reviewer: John Palmieri | Author: Volker Braun
Merged: | Dependencies:
-----------------------------+----------------------------------------------
Changes (by jhpalmieri):
* status: needs_review => needs_info
* reviewer: => John Palmieri
Old description:
> It would be convenient if quotient ring elements would be callable like
> polynomials. This is currently not the case:
> {{{
> sage: R.<x,y> = QQ[]
> sage: I = R.ideal(x)
> sage: Q = R.quotient_ring(I)
> sage: Q
> Quotient of Multivariate Polynomial Ring in x, y over Rational Field by
> the ideal (x)
> sage: Q.inject_variables()
> Defining xbar, ybar
> sage: p = xbar + ybar
> sage: p(1,1)
> ---------------------------------------------------------------------------
> TypeError Traceback (most recent call
> last)
>
> /home/vbraun/opt/sage-4.7.alpha4/devel/sage-main/<ipython console> in
> <module>()
>
> TypeError: 'QuotientRingElement' object is not callable
> }}}
>
> The attached patch implements this functionality by handing the argument
> through to the lift.
>
> Arguably, it should check that the result does not depend on the
> presentation. Pro: catches errors; Con: potentially slow, ideal
> membership test necessary if arguments are polynomials.
New description:
It would be convenient if quotient ring elements would be callable like
polynomials. This is currently not the case:
{{{
sage: R.<x,y> = QQ[]
sage: I = R.ideal(x)
sage: Q = R.quotient_ring(I)
sage: Q
Quotient of Multivariate Polynomial Ring in x, y over Rational Field by
the ideal (x)
sage: Q.inject_variables()
Defining xbar, ybar
sage: p = xbar + ybar
sage: p(1,1)
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/home/vbraun/opt/sage-4.7.alpha4/devel/sage-main/<ipython console> in
<module>()
TypeError: 'QuotientRingElement' object is not callable
}}}
The attached patch implements this functionality by handing the argument
through to the lift.
Arguably, it should check that the result does not depend on the
presentation. Pro: catches errors; Con: potentially slow, ideal membership
test necessary if arguments are polynomials.
---------
Apply [attachment:trac_11199-jhp.patch].
--
Comment:
Evaluating an element of a quotient ring doesn't make mathematical sense
in general, only if it makes sense to evaluate the lift: if you're taking
a quotient of a group algebra or the p-adics, what does it mean to
evaluate an element of it? I'm attaching a new patch which adds a comment
about this to the docstring; is this enough warning?
I'm happy with the original patch as far as it goes, and I'm almost ready
to give it a positive review, but I'd like to hear opinions about the
issue I raised.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/11199#comment:3>
Sage <http://www.sagemath.org>
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