#7580: bugs in infinite polynomial ring
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Reporter: was | Owner: SimonKing
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.3
Component: algebra | Keywords: infinite polynomial ring coercion
Work_issues: | Author: Simon King
Upstream: N/A | Reviewer:
Merged: |
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Comment(by SimonKing):
Replying to [comment:13 was]:
> sage: InfinitePolynomial(X,alpha_2)
> Expected:
> alpha_0
> Got:
> alpha_1
As I said, this test was supposed to demonstrate wrong usage, that occurs
due to an inconsistency in polynomial conversion. Both on my machine and
on sage.math, one gets
{{{
sage: A = ZZ['alpha_2','alpha_1','alpha_0']
sage: B.<alpha_3,alpha_1,alpha_2> = ZZ[]
sage: A(alpha_2)
alpha_0
sage: A(alpha_1)
alpha_1
sage: A(alpha_3)
alpha_2
}}}
So, the conversion is done by position of the variables. But when one has
one variable more, conversion is based on name:
{{{
sage: A2 = ZZ['alpha_2','alpha_1','alpha_0','foo']
sage: A2(alpha_2)
alpha_2
sage: A2(alpha_1)
alpha_1
sage: A2(alpha_3)
---------------------------------------------------------------------------
TypeError Traceback (most recent call
last)
...
TypeError:
}}}
I think this is documented somewhere. What happens on 32 bit Ubuntu?
Anyway. The purpose of this test was
1. make the user alert that a ''direct'' construction of elements of
infinite polynomial rings is not good -- one should use arithmetic on the
generators, or conversion.
2. Demonstrate that, in spite of the oddity of polynomial conversion,
''infinite'' polynomial conversion works fine.
But if the oddity of polynomial conversion is different on different
platforms (which I would then call a bug) then it might be better to just
drop that test. What do you think?
Cheers,
Simon
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7580#comment:16>
Sage <http://www.sagemath.org>
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