[Numpy-discussion] Re: Change definition of complex sign (and use it in copysign)

On Fri, 22 Dec 2023 at 13:25, <mhvk@astro.utoronto.ca> wrote:

Anyway, to me the main question would be whether this would break any workflows (though it is hard to see how it could, given that the previous definition was really rather useless...).

SymPy already defines sign(z) as z/abs(z) (with sign(0) = 0) as proposed here. Checking this I see that the current mismatch causes a bug when SymPy's lambdify function is used to evaluate the sign function with NumPy: In [12]: sign(z).subs(z, 1+1j) Out[12]: 0.707106781186548 + 0.707106781186548⋅ⅈ In [13]: lambdify(z, sign(z))(1+1j) # uses numpy Out[13]: (1+0j) The proposed change to NumPy's sign function would fix this bug. -- Oscar