[SciPy-User] problem with dot for complex matrices

Nils Wagner nwagner@iam.uni-stuttgart...
Tue Mar 27 13:58:26 CDT 2012


On Tue, 27 Mar 2012 13:48:14 -0500
  Ryan Krauss <ryanlists@gmail.com> wrote:
> I am loosing my mind while trying to debug some code.  I 
>am trying to
> find the cause of some differences between numpy 
>analysis and analysis
> done first in maxima and then converted to python code. 
> The maxima
> approach is more difficult to do, but seems to lead to 
>the correct
> answers.  The core issue seems to be one dot product of 
>a 2x2 and a
> 2x1 that are both complex numbers:
> 
> here is the 2x2:
> 
> ipdb> submatinv
> array([[-0.22740265-1.63857451j, 
>-0.07740957-0.55847886j],
>       [-3.20602957-4.93959054j, 
>-0.36746252-1.68352465j]])
> 
> here is the 2x1:
> 
> ipdb> augcol
> array([[ -3.74729148e-05-0.0005937j ],
>       [  7.96025801e-04+0.01137658j]])
> 
> verifying their shapes and data types:
> 
> ipdb> submatinv.shape
> (2, 2)
> ipdb> submatinv.dtype
> dtype('complex128')
> ipdb> augcol.shape
> (2, 1)
> ipdb> augcol.dtype
> dtype('complex128')
> 
> I need to compute this result:
> 
> ipdb> -1*numpy.dot(submatinv,augcol)
> array([[  5.30985737e-05+0.00038316j],
>       [  1.72370377e-04+0.00115503j]])
> 
> If I hard code how to do the matrix multiplication, I 
>get the correct
> answer (it agrees with Maxima):
> 
>For the first element:
> ipdb> 
>-1*(submatinv[0,0]*augcol[0,0]+submatinv[0,1]*augcol[1,0])
> (-0.005327660633034575+0.0011288088216130766j)
> 
>For the second
> ipdb> 
>-1*(submatinv[1,0]*augcol[0,0]+submatinv[1,1]*augcol[1,0])
> (-0.016047752110848554+0.003432076134378004j)
> 
> What is the dot product doing if it isn't dotting row by 
>column?
> 
> I am not seeing something.
> 
> Thanks,
> 
> Ryan
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> SciPy-User@scipy.org
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Hi Ryan,

I cannot reproduce your np.dot results, here.

python -i ryan_1.py
[[-0.00532766+0.00112881j]
  [-0.01604775+0.00343208j]]
1.7.0.dev-3503c5f

Nils
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