Leave sign of 0 unspecified for tanh inf + yj #1006

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1. kgryte commented on May 15, 2026

   

   kgryte

   on May 15, 2026

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   Thanks for raising this issue, @ndgrigorian. For complex number special handling, we deferred to behavior described in C99: https://en.cppreference.com/c/numeric/complex/ctanh. Namely,

   If z is +∞+yi (for any finite positive y), the result is 1+0i
   
2. ndgrigorian commented on May 15, 2026

   

   ndgrigorian

   on May 15, 2026

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   Thanks for raising this issue, @ndgrigorian. For complex number special handling, we deferred to behavior described in C99: https://en.cppreference.com/c/numeric/complex/ctanh. Namely,

   If z is +∞+yi (for any finite positive y), the result is 1+0i
   

   yes, but I would argue, that the cppreference page is a bit misleading as well. The ISO standard (final draft) text for C99 also uses sin(2y).

   NumPy also gives the same:

   import numpy as np
   
   print([np.tanh(complex(np.inf, n)) for n in range(4)])
   # [np.complex128(1+0j), np.complex128(1+0j), np.complex128(1-0j), np.complex128(1-0j)]
   

   at least for conda-forge NumPy, there can be discrepancies on PyPI with complex edge cases I've found.