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[Octave-bug-tracker] [bug #49291] residue function gives incompatible re

From: Rik
Subject: [Octave-bug-tracker] [bug #49291] residue function gives incompatible result
Date: Mon, 10 Oct 2016 18:16:53 +0000 (UTC)
User-agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:43.0) Gecko/20100101 Firefox/43.0

Follow-up Comment #9, bug #49291 (project octave):

@Marco: Thanks for testing.  Can you try another one from the BIST tests? 
This is from https://savannah.gnu.org/bugs/?34266.

 z1 =  7.0372976777e6;
 p1 = -3.1415926536e9;
 p2 = -4.9964813512e8;
 r1 = -(1 + z1/p1)/(1 - p1/p2)/p2/p1;
 r2 = -(1 + z1/p2)/(1 - p2/p1)/p2/p1;
 r3 = (1 + (p2 + p1)/p2/p1*z1)/p2/p1;
 r4 = z1/p2/p1;
 r = [r1; r2; r3; r4];
 p = [p1; p2; 0; 0];
 k = [];
 e = [1; 1; 1; 2];
 b = [1, z1];
 a = [1, -(p1 + p2), p1*p2, 0, 0];
 [br, ar] = residue (r, p, k)

If we eliminate all scrubbing code for small values then Octave returns a
value for br which is 1x4 where the first two entries are nearly zero.  If
Matlab does the same thing then we can be reasonably certain they are not
applying the filtering present in polyreduce.

There is still a possibility that they are replacing values less than eps(1)
with 0.  But first I want to see if Matlab returns a 1x4 vector for br.


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