On Thu, May 19, 2016 at 10:16 PM, <josef.p...@gmail.com> wrote: > > > 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 >
from __future__ import negative_power Josef > > Josef > > > >> Chuck >> >> >> _______________________________________________ >> NumPy-Discussion mailing list >> NumPy-Discussion@scipy.org >> https://mail.scipy.org/mailman/listinfo/numpy-discussion >> >> >
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