[Octave-bug-tracker] [bug #50124] cplxpair produces incorrect result for second column of complex pairs

[Rik]

Follow-up Comment #7, bug #50124 (project octave):

The function cplxpair is defined in an m-file.  If you look at the start of
the code there is a series of FIXME notes.


## FIXME: subsort returned pairs by imaginary magnitude
## FIXME: Why doesn't exp (2i*pi*[0:4]'/5) produce exact conjugates?  Does
## FIXME: it in Matlab?  The reason is that complex pairs are supposed
## FIXME: to be exact conjugates, and not rely on a tolerance test.


This seems relevant.  Also, with a high enough tolerance you can force Octave
to match pairs which are fairly far apart.  Octave does pair them, but returns
each half of the pair exactly as it appeared in the input.  If Matlab is
choosing to keep only one half of a pair and conjugate it to get the second
half, then this test will immediately show it.


z = [1 + 0.5i; 1; 1-0.49i]
cplxpair (z, 1e14)


The results for Octave are


octave:21> z = [1 + 0.5i; 1; 1-0.49i]
z =

   1.0000 + 0.5000i
   1.0000 + 0.0000i
   1.0000 - 0.4900i

octave:22> cplxpair (z, 1e14)
ans =

   1.0000 - 0.4900i
   1.0000 + 0.5000i
   1.0000 + 0.0000i



@Nicholas: Can you run the test code in Matlab to see what happens?



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