#6237: repeated roots with roots(CDF, multiplicities=False)
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Reporter: ncalexan | Owner: somebody
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.3.1
Component: basic arithmetic | Keywords: roots CDF multiplicities
Work_issues: | Author: Alex Ghitza
Upstream: N/A | Reviewer:
Merged: |
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Changes (by AlexGhitza):
* status: needs_info => needs_work
Comment:
Thanks for catching this.
From Pari's documentation for the function we're using:
{{{
polroots(pol,{flag = 0})
complex roots of the polynomial pol, given as a column vector where each
root is repeated according to its multiplicity. [...]
The algorithm used is a modification of A.Sch¨nhage's root-finding
algorithm, due to and implemented by X.Gourdon. Barring bugs, it is
guaranteed to converge and to give the roots to the required accuracy.
}}}
There is no mention of the roots being sorted. I guess I could read the
source code and find out, but I like you suggestion of sorting the Pari
output anyway -- just in case they change the behaviour in the future.
Also from the above snippet, Pari indeed does not give the multiplicities,
it just repeats each root the correct number of times.
I will replace the patch soon.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/6237#comment:3>
Sage <http://www.sagemath.org>
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