#10803: critical bug in real_roots
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Reporter: zimmerma | Owner: jason, jkantor
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-5.1
Component: numerical | Resolution:
Keywords: real roots, sd40.5 | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Paul Zimmermann | Merged in:
Dependencies: | Stopgaps:
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Comment (by zimmerma):
I believe I've found the reason for the bug: the function
{{{down_degree}}} decreases the
degree of the (interval) polynomial, but keeps the value {{{self.usign}}}.
With the example in the description and {{{seed=1}}}, {{{down_degree}}} is
called with:
{{{
enter down_degree, self= <IBP: ((34519150034, 25826190301, 17130808432,
9120071648, 2724478006, -830629355, 3694263) + [0 .. 21299)) * 2^-19 over
[3921/16384 .. 8017/32768]; level 2; slope_err [-136.91992834614365 ..
136.91992834614365]> usign= 1
}}}
and the polynomial is reduced to:
{{{
coeffs= (67412088, 41929949, 16504578, -2435470, -4640) n= 5
}}}
where it is clear that {{{usign=1}}} is wrong, since the sign of
{{{-4640}}} is -1.
Paul
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10803#comment:21>
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