#10483: Deprecate the misuse of symbolic variables as polynomial variable
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Reporter: SimonKing | Owner: AlexGhitza
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.6.1
Component: basic arithmetic | Keywords: deprecation symbolic polynomial
variable
Author: Simon King | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by SimonKing):
Replying to [comment:2 kcrisman]:
> Just a question - are the changes in symbolics because before the
variables might or might not have been strings?
As much as I know, the changes that I did in symbolics are indeed "replace
a variable `v` by `repr(v)` when it is used to define a polynomial ring.
> Also, is there an easy way to show what the generator of `P` would have
been in the "bad" old case? I think that's useful to point out, if one is
going to make the remarks in the first place.
I am not quite sure what you mean. By "remark", you probably mean
{{{
In earlier versions of Sage, the names have not necessarily been
strings. Some users provided a symbolic variable instead of a string,
and expected that this symbolic variable is the same as the generator
of the resulting polynomial ring, which is of course not the case.
This common mistake is now deprecated.
}}}
So, you suggest to write something like this:
{{{
In earlier versions of Sage, the names have not necessarily been
strings. Some users provided a symbolic variable instead of a string,
and expected that this symbolic variable is the same as the generator
of the resulting polynomial ring, which is of course not the case.
The following might be surpising for a user expecting the variable `x`
to be a polynomial::
sage: P = QQ['x'] # here, some users wrote QQ[x], which is now
deprecated
sage: x == P(x)
x == x
sage: type(x == P(x))
<type 'sage.symbolic.expression.Expression'>
sage: parent(x+P(x)) == P
False
}}}
I am not so convinced that the above text is good. Do you have a better
suggesion?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10483#comment:3>
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