NumPy，RuntimeWarning:在电源中遇到无效的值 [英] NumPy, RuntimeWarning: invalid value encountered in power

问题描述

我正在使用Python 3.6.
我真的很困惑，为什么会这样?

I am working with Python 3.6.
I am really confused, why this happened ?

In [1]: import numpy as np

In [2]: a = np.array(-1)

In [3]: a
Out[3]: array(-1)

In [4]: a ** (1/3)
/Users/wonderful/anaconda/bin/ipython:1: RuntimeWarning: invalid        value encountered in power
  #!/Users/wonderful/anaconda/bin/python
Out[4]: nan

推荐答案

Numpy似乎不允许负数的分数幂，即使该幂不会导致复数. (实际上，我今天早些时候也有同样的问题).一种解决方法是使用

Numpy does not seem to allow fractional powers of negative numbers, even if the power would not result in a complex number. (I actually had this same problem earlier today, unrelatedly). One workaround is to use

np.sign(a) * (np.abs(a)) ** (1 / 3)

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