[Octave-bug-tracker] [bug #50947] angle of -0-0i should be 0 for Matlab compatibility

[Rik]

Update of bug #50947 (project octave):

              Item Group:                    None => Matlab Compatibility   
                 Summary: angle of -0-0i should be 0 => angle of -0-0i should
be 0 for Matlab compatibility

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Follow-up Comment #2:

I think this is more of an issue about automatic narrowing and whether Matlab
keeps the sign bit on an IEEE 0.

Because storing complex numbers requires double the amount of storage (real
and imaginary 8-byte numbers), Octave automatically tries to compact to a real
array whenever the complex part is equal to zero.  Try the failing code in two
steps:


octave:1> x = -0-0i
x = -0
octave:2> angle (x)
ans =  3.1416
octave:3> angle (-x)
ans = 0


In the first stage, Octave compacts the value to '-0'.  And the angle of -0 is
pi.  Does Matlab keep the signbit for zero values?  What does the following
return in Matlab?


atan2 (0,0)
atan2 (0,-0)
atan2 (-0,-0)
atan2 (-0,0)


In Octave


octave:7> atan2 (0,0)
ans = 0
octave:8> atan2 (0,-0)
ans =  3.1416
octave:9> atan2 (-0,-0)
ans = -3.1416
octave:10> atan2 (-0,0)
ans = -0




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