Originally discussed in #153 (comment).

In order to add complex support to sign, we need to agree on the definition for complex numbers.

NumPy uses sqrt(z^2)/z while an arguably more common convention is x/|x|.

For paths forward we have 3 options:

1. Use NumPy's definition.
2. Use the more common convention used elsewhere (MATLAB, Julia, etc).
3. Not support complex numbers in sign.

Questions

• If we choose (2), given NumPy's potential v2 release, would NumPy be willing to introduce this breaking change?

See Also

• Add numpy.phase in addition to numpy.angle numpy/numpy#3621
• Ufuncs for complex numbers numpy/numpy#13179
• MATLAB: https://www.mathworks.com/help/matlab/ref/sign.html
• Julia: https://docs.julialang.org/en/v1/base/math/#Base.sign