On Thu, May 19, 2016 at 5:37 PM, Charles R Harris <charlesr.har...@gmail.com > wrote:
> Hi All, > > There are currently several pull requests apropos integer arrays/scalars > to integer powers and, because the area is messy and involves tradeoffs, > I'd like to see some discussion here on the list before proceeding. > > *Scalars in 1.10* > > In [1]: 1 ** -1 > Out[1]: 1.0 > > In [2]: int16(1) ** -1 > Out[2]: 1 > > In [3]: int32(1) ** -1 > Out[3]: 1 > > In [4]: int64(1) ** -1 > Out[4]: 1.0 > > In [5]: 2 ** -1 > Out[5]: 0.5 > > In [6]: int16(2) ** -1 > Out[6]: 0 > > In [7]: int32(2) ** -1 > Out[7]: 0 > > In [8]: int64(2) ** -1 > Out[8]: 0.5 > > In [9]: 0 ** -1 > --------------------------------------------------------------------------- > ZeroDivisionError Traceback (most recent call last) > <ipython-input-9-fd405d6cf4bc> in <module>() > ----> 1 0 ** -1 > > ZeroDivisionError: 0.0 cannot be raised to a negative power > > In [10]: int16(0) ** -1 > /home/charris/.local/bin/ipython:1: RuntimeWarning: divide by zero > encountered in power > #!/usr/bin/python > /home/charris/.local/bin/ipython:1: RuntimeWarning: invalid value > encountered in power > #!/usr/bin/python > Out[10]: -9223372036854775808 > > In [11]: int32(0) ** -1 > Out[11]: -9223372036854775808 > > In [12]: int64(0) ** -1 > /home/charris/.local/bin/ipython:1: RuntimeWarning: divide by zero > encountered in long_scalars > #!/usr/bin/python > Out[12]: inf > > Proposed > > - for non-zero numbers the return type should be float. > - for zero numbers a zero division error should be raised. > > > > > *Scalar Arrays in 1.10* > In [1]: array(1, dtype=int16) ** -1 > Out[1]: 1 > > In [2]: array(1, dtype=int32) ** -1 > Out[2]: 1 > > In [3]: array(1, dtype=int64) ** -1 > Out[3]: 1 > > In [4]: array(2, dtype=int16) ** -1 > Out[4]: 0 > > In [5]: array(2, dtype=int32) ** -1 > Out[5]: 0 > > In [6]: array(2, dtype=int64) ** -1 > Out[6]: 0 > > In [7]: array(0, dtype=int16) ** -1 > /home/charris/.local/bin/ipython:1: RuntimeWarning: divide by zero > encountered in power > #!/usr/bin/python > /home/charris/.local/bin/ipython:1: RuntimeWarning: invalid value > encountered in power > #!/usr/bin/python > Out[7]: -9223372036854775808 > > In [8]: array(0, dtype=int32) ** -1 > Out[8]: -9223372036854775808 > > In [9]: array(0, dtype=int64) ** -1 > Out[9]: -9223372036854775808 > > In [10]: type(array(1, dtype=int64) ** -1) > Out[10]: numpy.int64 > > In [11]: type(array(1, dtype=int32) ** -1) > Out[11]: numpy.int64 > > In [12]: type(array(1, dtype=int16) ** -1) > Out[12]: numpy.int64 > > Note that the return type is always int64 in all these cases. However, > type is preserved in non-scalar arrays, although the value of int16 is not > compatible with int32 and int64 for zero division. > > In [22]: array([0]*2, dtype=int16) ** -1 > Out[22]: array([0, 0], dtype=int16) > > In [23]: array([0]*2, dtype=int32) ** -1 > Out[23]: array([-2147483648, -2147483648], dtype=int32) > > In [24]: array([0]*2, dtype=int64) ** -1 > Out[24]: array([-9223372036854775808, -9223372036854775808]) > > Proposed: > > - Raise an ZeroDivisionError for zero division, that is, in the ufunc. > - Scalar arrays to return scalar arrays > > > Thoughts? > Why does negative exponent not upcast to float like division? sounds like python 2 to me Josef > Chuck > > > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > https://mail.scipy.org/mailman/listinfo/numpy-discussion > >
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