[Numpy-discussion] Behaviour of integer powers

Stéfan van der Walt stefan@sun.ac...
Sun Feb 8 03:54:04 CST 2009


Hi all,

Ticket #955 (http://scipy.org/scipy/numpy/ticket/955) touches on the
following issue:

>>> 0.0 ** np.array([-1, 0, 1], dtype=np.int32)
array([ Inf,   1.,   0.])
>>> 0.0 ** np.array([-1, 0, 1], dtype=np.int32)[0]
------------------------------------------------------------
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
ZeroDivisionError: 0.0 cannot be raised to a negative power

This is on a 32-bit platform.

As I understand this happens because, in the second case, Python sees
that "-1" is an int and does the power operation.  In other words,
when we raise to the power of an array, the NumPy machinery is
involved, whereas if we raise to np.int32(-1), it is not.  This is due
to the int32 type deriving from the Python int.

I can't think of an easy way to address the problem, but I was hoping
to get some advice from the list.

Thanks
Stéfan


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