#17971: Infinite recursion when taking a resultant over a complicated base ring
-------------------------------------+-------------------------------------
Reporter: pbruin | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.6
Component: algebra | Resolution:
Keywords: infinite | Merged in:
recursion polynomial resultant | Reviewers:
Authors: Peter Bruin | Work issues:
Report Upstream: N/A | Commit:
Branch: | da8ddc1c1e9b3f9867f0fe74beda90f16244b2b5
u/pbruin/17971-infinite_recursion | Stopgaps:
Dependencies: |
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Description changed by pbruin:
Old description:
> The following resultant computation leads to an infinite recursion:
> {{{
> sage: A.<a,c> = Frac(PolynomialRing(QQ,'a,c'))
> sage: B.<d,e> = PolynomialRing(A,'d,e')
> sage: R.<x> = PolynomialRing(B,'x')
> sage: (a*d*x^2+a+e+1).resultant(-4*c^2*x+1)
> Traceback (most recent call last):
> ...
> RuntimeError: maximum recursion depth exceeded while calling a Python
> object
> }}}
> We solve this by replacing a recursive call in
> `FractionField_generic._element_constructor_()` by a more direct
> construction of the element.
>
> (This is independent of #17817.)
New description:
The following resultant computation leads to an infinite recursion:
{{{
sage: A.<a,c> = Frac(PolynomialRing(QQ,'a,c'))
sage: B.<d,e> = PolynomialRing(A,'d,e')
sage: R.<x> = PolynomialRing(B,'x')
sage: (a*d*x^2+a+e+1).resultant(-4*c^2*x+1)
Traceback (most recent call last):
...
RuntimeError: maximum recursion depth exceeded while calling a Python
object
}}}
We solve this by replacing a recursive call in
`FractionField_generic._element_constructor_()` by a more direct
construction of the element.
This particular bug is also fixed (in a different way) by #17974, but the
doctest and the shortcut added by this ticket are useful regardless of
that.
--
--
Ticket URL: <http://trac.sagemath.org/ticket/17971#comment:2>
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