[Numpy-discussion] Re: indexing problem
Tim Hochberg
tim.hochberg at cox.net
Mon Feb 13 11:31:05 CST 2006
I've been trying to look into the problem described below, but I just
can't find where complex multiplication is being done (all the other
multiplication, but not complex). Could someone with a grasp of the
innards of numpy please point me in the right direction?
Thanks,
-tim
Ryan Krauss wrote:
>This may only be a problem for ridiculously large numbers. I actually
>meant to be dealing with these values:
>
>In [75]: d
>Out[75]:
>array([ 246.74011003, 986.96044011, 2220.66099025, 3947.84176044,
> 6168.50275068, 8882.64396098, 12090.26539133, 15791.36704174,
> 19985.94891221, 24674.01100272])
>
>In [76]: s=d[-1]*1.0j
>
>In [77]: s
>Out[77]: 24674.011002723393j
>
>In [78]: type(s)
>Out[78]: <type 'complex128scalar'>
>
>In [79]: s**2
>Out[79]: (-608806818.96251547+7.4554869875188623e-08j)
>
>So perhaps the previous difference of 26 orders of magnitude really
>did mean that the imaginary part was negligibly small, that just got
>obscured by the fact that the real part was order 1e+135.
>
>On 2/13/06, Ryan Krauss <ryanlists at gmail.com> wrote:
>
>
>>I am having a problem with indexing an array and not getting the
>>expected scalar behavior for complex128scalar:
>>
>>In [44]: c
>>Out[44]:
>>array([ 3.31781200e+06, 2.20157529e+13, 1.46088259e+20,
>> 9.69386754e+26, 6.43248601e+33, 4.26835585e+40,
>> 2.83232045e+47, 1.87942136e+54, 1.24711335e+61,
>> 8.27537526e+67])
>>
>>In [45]: s=c[-1]*1.0j
>>
>>In [46]: type(s)
>>Out[46]: <type 'complex128scalar'>
>>
>>In [47]: s**2
>>Out[47]: (-6.848183561893313e+135+8.3863291020365108e+119j)
>>
>>In [48]: s=8.27537526e+67*1.0j
>>
>>In [49]: type(s)
>>Out[49]: <type 'complex'>
>>
>>In [50]: s**2
>>Out[50]: (-6.8481835693820068e+135+0j)
>>
>>Why does result 47 have a non-zero imaginary part?
>>
>>Ryan
>>
>>
>>
>
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