[Numpy-discussion] weird problem with subtracting ndarrays
Wed Jun 12 14:30:49 CDT 2013
On Wed, Jun 12, 2013 at 3:25 PM, Moroney, Catherine M (398D)
> I've got two arrays of the same shape that I read in from a file, and I'm trying to
> difference them. Very simple stuff, but I'm getting weird answers.
> Here is the code:
>>>> counts1 = hfile1.read_grid_field("CFbA", "TerrainReferencedRCCMFraction_Num")
>>>> counts2 = hfile2.read_grid_field("CFbA", "TerrainReferencedRCCMFraction_Num")
>>>> counts1.max(), counts2.max()
> (13, 13)
>>>> counts1.min(), counts2.min()
> (0, 0)
>>>> numpy.all(counts1 == counts2)
>>>> diff = counts1 - counts2
> 4294967295 !! WHAT IS HAPPENING HERE ??
>>>> sum = counts1 + counts2
> As you can see, the range of values in both arrays is 0 to 13, and the sum
> behaves normally, but the difference gives this weird number.
> When I create dummy arrays, the subtraction works fine. So there must be some funny value
> lurking in either the counts1 or counts2 array, but the numpy.isnan() test returns False.
> Any ideas for how I debug this?
check the dtype of the count variables, may be uint
diff =1 * counts1 - counts2
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