numpy-discussion

[Numpy-discussion] Bug? Product of complex arrays

[Aureli S. F. <Aur...@ip...>]

Hi,

It seems there is a problem when multiplying complex arrays, but maybe that
is already solved for the new NumPy 17.3, is it?

The product of complex arrays does not seem to be right.

Code lines:

>>> a=a_conj[:]
>>> a
array([[ 1.-0.j,  1.-1.j,  1.-2.j],
       [ 1.-3.j,  1.-4.j,  1.-5.j],
       [ 1.-6.j,  1.-7.j,  1.-8.j]])
>>> a.imag=a.imag*-1
>>> a
array([[ 1.+0.j,  1.+1.j,  1.+2.j],
       [ 1.+3.j,  1.+4.j,  1.+5.j],
       [ 1.+6.j,  1.+7.j,  1.+8.j]])
>>> Numeric.multiply(a,a_conj)
array([[  1. +0.j,   0. +2.j,  -3. +4.j],
       [ -8. +6.j, -15. +8.j, -24.+10.j],
       [-35.+12.j, -48.+14.j, -63.+16.j]])

where the answer should be [[1+0j,2+0j,5+0j][10+0j,...

#################################
Aureli Soria Frisch
Fraunhofer IPK
Dept. Pattern Recognition

post: Pascalstr. 8-9, 10587 Berlin, Germany
e-mail:au...@ip...
fon: +49 30 39 00 61 50
fax: +49 30 39 17 517
#################################

Re: [Numpy-discussion] Bug? Product of complex arrays

[Tim H. <tim...@ie...>]

From: "Aureli Soria Frisch" <Aur...@ip...>



> Hi,
>
> It seems there is a problem when multiplying complex arrays, but maybe
that
> is already solved for the new NumPy 17.3, is it?
>
> The product of complex arrays does not seem to be right.
>
> Code lines:
>
> >>> a=a_conj[:]

This is your problem here. Array's differ from lists and such in that
slicing does not produce a copy. 'a' and 'a_conj' point to the same data
after this operation. One way to produce a copy is to use 'a =
Numeric.array(a_conj)'

> >>> a
> array([[ 1.-0.j,  1.-1.j,  1.-2.j],
>        [ 1.-3.j,  1.-4.j,  1.-5.j],
>        [ 1.-6.j,  1.-7.j,  1.-8.j]])
> >>> a.imag=a.imag*-1
> >>> a
> array([[ 1.+0.j,  1.+1.j,  1.+2.j],
>        [ 1.+3.j,  1.+4.j,  1.+5.j],
>        [ 1.+6.j,  1.+7.j,  1.+8.j]])

If you look at a_conj  now, you should see that it is the same as a.

> >>> Numeric.multiply(a,a_conj)
> array([[  1. +0.j,   0. +2.j,  -3. +4.j],
>        [ -8. +6.j, -15. +8.j, -24.+10.j],
>        [-35.+12.j, -48.+14.j, -63.+16.j]])

So what you have here is really a squared.

So, you could get this to work by replacing slicing with array(a_conf). A
much simpler way is:

a = Numeric.conjugate(a_conj)
a*a_conj
#...

Hope that clears things up for you.

-tim



> where the answer should be [[1+0j,2+0j,5+0j][10+0j,...
>
> #################################
> Aureli Soria Frisch
> Fraunhofer IPK
> Dept. Pattern Recognition
>
> post: Pascalstr. 8-9, 10587 Berlin, Germany
> e-mail:au...@ip...
> fon: +49 30 39 00 61 50
> fax: +49 30 39 17 517
> #################################
>
>
>
> _______________________________________________
> Numpy-discussion mailing list
> Num...@li...
> http://lists.sourceforge.net/lists/listinfo/numpy-discussion