[Numpy-discussion] f.p. powers and masked arrays

Michael Fitzgerald fitz at astron.berkeley.edu
Wed Jun 21 23:39:51 CDT 2006


Hello all,

I'm encountering some (relatively new?) behavior with masked arrays that 
strikes me as bizarre.  Raising zero to a floating-point value is triggering 
a mask to be set, even though the result should be well-defined.  When using 
fixed-point integers for powers, everything works as expected.  I'm seeing 
this with both numarray and numpy.  Take the case of 0**1, illustrated below:

>>> import numarray as n1
>>> import numarray.ma as n1ma
>>> n1.array(0.)**1
array(0.0)
>>> n1.array(0.)**1.
array(0.0)
>>> n1ma.array(0.)**1
array(0.0)
>>> n1ma.array(0.)**1.
array(data =
 [1.0000000200408773e+20],
      mask =
 1,
      fill_value=[  1.00000002e+20])

>>> import numpy as n2
>>> import numpy.core.ma as n2ma
>>> n2.array(0.)**1
array(0.0)
>>> n2.array(0.)**1.
array(0.0)
>>> n2ma.array(0.)**1
array(0.0)
>>> n2ma.array(0.)**1.
array(data =
 1e+20,
      mask =
 True,
      fill_value=1e+20)

I've been using python v2.3.5 & v.2.4.3, numarray v1.5.1, and numpy v0.9.8, 
and tested this on an x86 Debian box and a PPC OSX box.  It may be the case 
that this issue has manifested in the past several months, as it's causing a 
new problem with some of my older code.  Any thoughts?

Thanks in advance,
Mike





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