#13645: PolynomialRing variables are not generic symbolic variables
---------------------------------+------------------------------------------
Reporter: llpamies | Owner: burcin
Type: defect | Status: needs_review
Priority: trivial | Milestone: sage-5.4
Component: symbolics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Burcin Erocal | Merged in:
Dependencies: | Stopgaps:
---------------------------------+------------------------------------------
Changes (by {'newvalue': u'Burcin Erocal', 'oldvalue': ''}):
* priority: major => trivial
* reviewer: Burcin Erocal =>
* milestone: sage-duplicate/invalid/wontfix => sage-5.4
* author: => Burcin Erocal
Old description:
> Consider the following Sage code:
>
> {{{
> sage: a,b=var('a,b')
> sage: solve([a+b+a*b == 1], a)
> [a == -(b - 1)/(b + 1)]
> }}}
>
> If I want to do something similar with elements of a PolynomialRing the
> code crashes:
> {{{
> sage: poly.<a,b> = PolynomialRing(RR)
> sage: solve([a+b+a*b == 1], a)
> }}}
New description:
Consider the following Sage code:
{{{
sage: a,b=var('a,b')
sage: solve([a+b+a*b == 1], a)
[a == -(b - 1)/(b + 1)]
}}}
If I want to do something similar with elements of a PolynomialRing the
code crashes:
{{{
sage: poly.<a,b> = PolynomialRing(RR)
sage: solve([a+b+a*b == 1], a)
}}}
Apply: [attachment:trac_13645-solve_input_handling.patch]
--
Comment:
OK. I attached a patch to fix the error message. Now we have:
{{{
sage: poly.<a,b> = PolynomialRing(RR)
sage: solve([a+b+a*b == 1], a)
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
/home/burcin/sage/sage-5.2/<ipython console> in <module>()
/home/burcin/sage/sage-5.2/local/lib/python2.7/site-
packages/sage/symbolic/relation.pyc in solve(f, *args, **kwds)
681 return f[0].solve(*args,**kwds)
682 # otherwise complain
--> 683 raise TypeError("The first argument to solve() should be a
symbolic expression or a list of symbolic expressions, cannot handle
%s"%repr(type(f[0])))
684
685 # f is a list of such expressions or equations
TypeError: The first argument to solve() should be a symbolic expression
or a list of symbolic expressions, cannot handle <type 'bool'>
}}}
Please review.
Replying to [comment:2 llpamies]:
> If you say that,
> > The comparison operator for polynomial rings is important (think
monomial orders and Groebner bases), we cannot change it to keep the
relations symbolic.
>
> Shouldn't Sage raise an exception when evaluating "a+b+a*b == 1", saying
something like "Symbolic comparisons are not allowed for polynomial
rings.", instead of returning False.
No, that operations checks for equality of polynomials. That polynomial is
not equal to `1`. As I wrote before, we cannot modify the comparison of
polynomials.
> And besides that, why is "solve([False], a)" raising such a
incomprehensible "TypeError" exception ?
This was caused by a typo. Python was complaining about a different issue
when it said `TypeError: not all arguments converted during string
formatting`. I hope the new error message is more useful.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13645#comment:3>
Sage <http://www.sagemath.org>
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