#8555: Unexpected behaviour of symbolic zero.
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Reporter: lfousse | Owner: burcin
Type: defect | Status: needs_review
Priority: major | Milestone:
Component: symbolics | Resolution:
Keywords: | Merged in:
Authors: André Apitzsch | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/aapitzsch/ticket/8555 | c79c0fb678fb6e7f27a966ce7fbadfae258aa3c0
Dependencies: | Stopgaps:
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Comment (by nbruin):
Perhaps it's better to be a bit more selective than just avoiding the zero
shortcut completely. It's only `SR(0)` that has this funny behaviour. All
other zeros should be fine. So the test should probably be something like
{{{
if not isinstance(right, sage.symbolic.expression.Expression) and
right == 0:
return bool(self._MPolynomial_element__element)
}}}
Note the chance to the if body.
This return value evaluates slightly faster when `self` is in fact 0 and a
lot faster if `self` is nonzero (I suspect it kicks down to checking if
`self._MPolynomial_element__element.__len__()` is 0, but does so on
CPython slot level, so saves quite a bit of lookup).
It's of course nice to try and make symbolic entities work consistently
with MPolynomial, but interacting with SR is not the main purpose of
MPolynomial, so you should make sure that measures undertaken for it do
not affect other use cases.
I don't have an immediate answer on what the best way is to make available
the symbol `sage.symbolic.expression.Expression` (or what the best test is
determine reliably and cheaply whether `right` is an element of SR). One
way is of course to just `import sage.symbolic.expression`, but it's a
little unfortunate to create an apparent dependence (even if that's a
circular import, it should be fine, though). Doing the import in the
method is not an option.
--
Ticket URL: <http://trac.sagemath.org/ticket/8555#comment:3>
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