From bug-octave-request at bevo dot che dot wisc dot edu  Mon Nov  8 10:36:26 1999
Subject: Test fails - octave-2.1.20 on irix6.5
From: "Billinghurst, David (RTD)" <David dot Billinghurst at riotinto dot com dot au>
To: bug-octave at bevo dot che dot wisc dot edu
Date: Mon, 8 Nov 1999 10:36:23 -0600 (CST)

Just built octave-2.1.20 on irix6.5 with both gcc-2.95.1 and egcs 19991102
snapshot.

I get a failure on test poly/residue-1.m as it misses the allowed tolerances

by an order of magnitude. Haven't done a full error analysis, but I suspect 
the tolerances may be a little tight.

The test case poly/residue-1.m is

b = [1, 1, 1];
a = [1, -5, 8, -4];
[r, p, k, e] = residue (b, a);
(abs (r - [-2; 7; 3]) < sqrt (eps)
 && abs (p - [2; 2; 1]) < sqrt (eps)
 && isempty (k)
 && e == [1; 2; 1])

For octave-2.1.20 this fails as 

r - [-2; 7; 3]  = 
   -1.0658e-14
    1.7276e-07
    1.1990e-14

while sqrt (eps) =  1.4901e-08

The difference occurs at the start of residue in the calculation of
roots(a)
 
For octave-2.0.14 we have 

roots([1, -5, 8, -4])
ans =

  2.000000000000000 + 0.000000044133310i
  2.000000000000000 - 0.000000044133310i
  0.999999999999999 + 0.000000000000000i

while for octave-2.1.20 we have

roots([1, -5, 8, -4])
ans =

  2.00000008638208
  1.99999991361792
  1.00000000000000

Either:
  roots() is inaccurate (wrong), or
  the tolerances on r are too tight
In either case residue() itself is OK.



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