[Octave-bug-tracker] [bug #60786] mpower: negative scalar to power of matrix containing non-integers returns nan

[John W. Eaton]

Follow-up Comment #19, bug #60786 (project octave):

@rik: Yes, definitely a bummer.  I'm tempted to use our own "oct-math.h" and
"oct-complex.h" that would provide all the math functions that we need with
the behavior we want.  Then we would also not allow the standard header files
to be included directly in Octave's source files and we could at least ensure
consistency in Octave functions.  But of course that doesn't "fix" the
behavior of other dependencies that we have.

If we don't override the complex pow function to do what we want we *will*
have to check all places where it is used.  I've been looking at the
element-wise operations in sparse-xpow.cc and it first checks whether
conversion to complex is needed for any of the calculations, and if so just
uses complex pow for all.  But then that can produce these "bad" results:


octave> x = sparse ([-2, 0, -2]);
octave> y = sparse ([-2, 0, 0.25]);
octave> x .^ y
ans =

Compressed Column Sparse (rows = 1, cols = 3, nnz = 3 [100%])

  (1, 1) ->  2.5000e-01 + 6.1232e-17i
  (1, 2) ->  1 + 0i
  (1, 3) ->  0.8409 + 0.8409i



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