#10803: critical bug in real_roots
--------------------------------------+-------------------------------------
Reporter: zimmerma | Owner: jason, jkantor
Type: defect | Status: closed
Priority: critical | Milestone: sage-5.5
Component: numerical | Resolution: fixed
Keywords: real roots, sd40.5 | Work issues:
Report Upstream: N/A | Reviewers: Jeroen Demeyer
Authors: Paul Zimmermann | Merged in: sage-5.4.1.rc0
Dependencies: | Stopgaps:
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Changes (by jdemeyer):
* merged: sage-5.5.beta0 => sage-5.4.1.rc0
Old description:
> This was reported on http://groups.google.com/group/sage-
> support/msg/6a7c93ad16b892bf:
> {{{
> sage: from sage.rings.polynomial.real_roots import real_roots
> sage: x = polygen(QQ)
> sage: f = 2503841067*x^13 - 15465014877*x^12 + 37514382885*x^11 -
> 44333754994*x^10 + 24138665092*x^9 - 2059014842*x^8 - 3197810701*x^7 +
> 803983752*x^6 + 123767204*x^5 - 26596986*x^4 - 2327140*x^3 + 75923*x^2 +
> 7174*x + 102
> sage: len(real_roots(f)), len(real_roots(f,strategy='warp'))
> (11, 13)
> }}}
> It seems different seeds give different numbers of roots:
> {{{
> sage: len(real_roots(f,seed=1))
> 11
> sage: len(real_roots(f,seed=3))
> 13
> }}}
> I mark this as blocker since counting properly the number of real
> roots of a polynomial is a very basic thing for a computer algebra
> system.
>
> Paul
New description:
This was reported on http://groups.google.com/group/sage-
support/msg/6a7c93ad16b892bf:
{{{
sage: from sage.rings.polynomial.real_roots import real_roots
sage: x = polygen(QQ)
sage: f = 2503841067*x^13 - 15465014877*x^12 + 37514382885*x^11 -
44333754994*x^10 + 24138665092*x^9 - 2059014842*x^8 - 3197810701*x^7 +
803983752*x^6 + 123767204*x^5 - 26596986*x^4 - 2327140*x^3 + 75923*x^2 +
7174*x + 102
sage: len(real_roots(f)), len(real_roots(f,strategy='warp'))
(11, 13)
}}}
It seems different seeds give different numbers of roots:
{{{
sage: len(real_roots(f,seed=1))
11
sage: len(real_roots(f,seed=3))
13
}}}
--
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10803#comment:27>
Sage <http://www.sagemath.org>
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