[Numpy-discussion] Bizarre errors with byteswapping, complex256, PPC

Travis Oliphant travis@continuum...
Wed Jun 20 17:04:37 CDT 2012


That is clearly wrong and worth a bug report.

Travis 

--
Travis Oliphant
(on a mobile)
512-826-7480


On Jun 20, 2012, at 5:00 PM, Matthew Brett <matthew.brett@gmail.com> wrote:

> Hi,
> 
> On Wed, Jun 20, 2012 at 1:56 PM, Travis Oliphant <travis@continuum.io> wrote:
>> This looks like a problem with comparisons of floating point numbers rather than a byteswapping problem per-say.   Try to use an almost equal comparison instead.
> 
> Is that right - that the byteswapped versions might not be strictly
> equal to identical numbers but not byteswapped?
> 
> But I should maybe have been clearer - they also subtract wrongly:
> 
> <script>
> import numpy as np
> 
> arr = np.arange(10, dtype=np.complex256)
> bs_arr = arr.byteswap().newbyteorder('S')
> print arr
> print bs_arr
> print arr - bs_arr
> print arr - bs_arr
> print arr - bs_arr
> </script>
> 
> (np-devel)[mb312@joshlegacy ~/tmp]$ python funny_bs.py
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> 
> (wrong)
> 
> (np-devel)[mb312@joshlegacy ~/tmp]$ python funny_bs.py
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> [ 0.0+0.0j  1.0+0.0j  2.0+0.0j  3.0+0.0j  4.0+0.0j  5.0+0.0j  6.0+0.0j
>  7.0+0.0j  8.0+0.0j  9.0+0.0j]
> [ 0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j
>  0.0+0.0j  0.0+0.0j  0.0+0.0j]
> [ 0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j
>  0.0+0.0j  0.0+0.0j  0.0+0.0j]
> [ 0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j  0.0+0.0j
>  0.0+0.0j  0.0+0.0j  0.0+0.0j]
> 
> (right)
> 
> See you,
> 
> Matthew
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