#16894: bug in is_square over number fields
-------------------------+-------------------------------------------------
Reporter: cremona | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: number | Keywords:
fields | Authors:
Merged in: | Report Upstream: Fixed upstream, but not in a
Reviewers: | stable release.
Work issues: | Branch:
Commit: | Dependencies:
Stopgaps: |
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A precision bug in pari 2.7.1 causes this:
{{{
sage: K.<a> = QuadraticField(22)
sage: u = 42*a - 197 # fundamental unit
sage: D = u^14
sage: D.is_square()
MemoryError: Unable to allocate 327680000000 bytes for the PARI stack
(instead, allocated 262144000000 bytes)
}}}
This was reported upstream (to Karim Belabas) who fixed it in pari's main
development branch 2.8.*. It would be good to get the bug fix into Sage
sooner.
From Karim's email:
{{{
Not a memory issue indeed. The low-level function from the polroots
module that (sharply) estimates the largest modulus of a polynomial
T can't handle the case T(0) = 0 (nor the case where T is constant,
but that's not the issue here...).
It never occurs in the original context of polroots(), but it can occur
in the context of nfroots / nffactor that call it with T := the image
through the successive complex embeddings of our algebraic polynomial.
Fixed in master (2.8.*). Thanks for your report !
}}}
--
Ticket URL: <http://trac.sagemath.org/ticket/16894>
Sage <http://www.sagemath.org>
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