#18360: handle mutable objects better in symbolic evaluation
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Reporter: rws | Owner:
Type: enhancement | Status: new
Priority: major | Milestone: sage-6.8
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Changes (by rws):
* cc: nbruin (added)
* milestone: sage-6.7 => sage-6.8
Old description:
> In examples like this:
> {{{
> sage: f(x)=matrix()
> sage: bool(f(x)-f(x)==0)
> ...
> TypeError: mutable matrices are unhashable
> }}}
> the `f(x)` is expanded into a mutable matrix, but this prevents
> evaluation because Pynac is called by `Expression._sub_` and wants to do
> hashes on the matrix for comparison reasons. However, for the purpose of
> subtraction dealing with a mutable matrix is completely unnecessary. So a
> solution would be to turn mutable objects immutable before doing
> arithmetics in `Expression` or in Pynac.
New description:
In examples like this:
{{{
sage: f(x)=matrix()
sage: bool(f(x)-f(x)==0)
...
TypeError: mutable matrices are unhashable
}}}
the `f(x)` is expanded into a mutable matrix, but this prevents evaluation
because Pynac is called by `Expression._sub_` and wants to do hashes on
the matrix for comparison reasons. However, for the purpose of subtraction
dealing with a mutable matrix is completely unnecessary. So a solution
would be to turn mutable objects immutable before doing arithmetics in
`Expression` or in Pynac.
While the most elegant solution to the specific problem would be an
expression converter, applied before calling Pynac's `relational_to_bool`
this will not solve other instances like
{{{
sage: f(x)=matrix(ZZ, 8)
sage: f(x)*1
...
TypeError: mutable matrices are unhashable
}}}
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Ticket URL: <http://trac.sagemath.org/ticket/18360#comment:1>
Sage <http://www.sagemath.org>
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