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Editorial Team
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Asked: 2026-05-22T23:41:57+00:00

Perhaps this is an algorithmic issue, but the following piece of code numpy.power((-1+0j),0.5) produces

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Perhaps this is an algorithmic issue, but the following piece of code

numpy.power((-1+0j),0.5)

produces the following output

(6.1230317691118863e-17+1j)

Analogous expressions e.g. numpy.power(complex(-1),.5) yield the same result, however – numpy.sqrt(complex(-1)) yields the expected result of 1j. Clearly the result should have no real part, so I am missing something crucial or do I need to report this to numpy dev’s.

In case anyone asks, no I can not round away the real part (I need full precision for this calculation) and yes I need to use the power function.

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1 Answer

  1. Editorial Team

    It’s a side effect of the implementation of numpy.power() for complex numbers. The stdlib exhibits the same issue.

    >>> numpy.power(-1+0j, 0.5)
(6.123233995736766e-17+1j)
>>> cmath.exp(cmath.log(-1)/2)
(6.123233995736766e-17+1j)
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