[Octave-bug-tracker] [bug #53869] Residue returning an inaccurate result

[Rik]

Follow-up Comment #7, bug #53869 (project octave):

I think this is the correct thing to do.  However, when I make the change and
then run "test residue" I get a failure in the BIST tests.


octave:14> test residue
***** test
 b = [1, 0, 1];
 a = [1, 0, 18, 0, 81];
 [r, p, k, e] = residue (b, a);
 r1 = [-5i; 12; +5i; 12]/54;
 p1 = [+3i; +3i; -3i; -3i];
 assert (r, r1, 1e-12);
 assert (p, p1, 1e-12);
 assert (isempty (k));
 assert (e, [1; 2; 1; 2]);
 [br, ar] = residue (r, p, k);
 assert (br, [0,b], 1e-12);
 assert (ar, a, 1e-12);
!!!!! test failed
ASSERT errors for:  assert (br,[0, b],1e-12)

  Location  |  Observed  |  Expected  |  Reason
     .          O(1x3)       E(1x4)      Dimensions don't match


The issue is that the call


 [br, ar] = residue (r, p, k);


used produce a 4-element vector


[ 0, 1, 0, 1]


Now it produces just a 3-element vector 


[ 1, 0, 1]


Given that this vector represents a polynomial, it seems better that the
leading 0 should be removed.

@Tony: Could you check that Matlab produces a 3-element vector for the code
above?


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