# [SciPy-dev] Trouble with sparse complex matrices

Robert Cimrman cimrman3 at ntc.zcu.cz
Mon Oct 9 04:51:28 CDT 2006

```Nils Wagner wrote:
>  Hi all,
>
> I have constructed a 2x2 lil_matrix and added some complex values to it.
> The imaginary is neglected for some reason.
>
> from scipy import *
> A = sparse.lil_matrix((2,2))
> A[:,1] = random.rand(2)+1j*random.rand(2)
> A[1,:] = random.rand(2)+1j*random.rand(2)
> print A.real
> print A.imag
> print A
> A = A.todense()
> print 'The imiginary part of A is missing'
> print A
>

In [1]:A = sp.lil_matrix((2,2))
In [2]:A
Out[2]:
<2x2 sparse matrix of type '<type 'numpy.float64'>'
with 0 stored elements in LInked List format>

In [3]:A[:,1] = rand(2)+1j*rand(2)
In [4]:A[1,:] = rand(2)+1j*rand(2)
In [8]:A
Out[8]:
<2x2 sparse matrix of type '<type 'numpy.float64'>'
with 3 stored elements in LInked List format>

--------------------
- so here the type of the matrix is still real! I think you have found
another bug... In the meantime, you can use the code below:
--------------------

In [15]:A = sp.lil_matrix((2,2), dtype = nm.complex128)

In [16]:A
Out[16]:
<2x2 sparse matrix of type '<type 'numpy.complex128'>'
with 0 stored elements in LInked List format>

In [17]:A[:,1] = rand(2)+1j*rand(2)

In [18]:A[1,:] = rand(2)+1j*rand(2)

In [19]:A
Out[19]:
<2x2 sparse matrix of type '<type 'numpy.complex128'>'
with 3 stored elements in LInked List format>

In [20]:print A
(0, 1)        (0.958469152451+0.477931946516j)
(1, 0)        (0.945332109928+0.92267626524j)
(1, 1)        (0.734181404114+0.921519994736j)

In [21]:A.real
Out[21]:
<2x2 sparse matrix of type '<type 'numpy.float64'>'
with 3 stored elements (space for 3)
in Compressed Sparse Column format>

In [22]:print A.real
(1, 0)        0.945332109928
(0, 1)        0.958469152451
(1, 1)        0.734181404114

In [23]:print A.imag
(1, 0)        0.92267626524
(0, 1)        0.477931946516
(1, 1)        0.921519994736

In [24]:A = A.todense()

In [25]:print A
[[  0.00000000e+00+0.j           9.58469152e-01+0.47793195j]
[  9.45332110e-01+0.92267627j   7.34181404e-01+0.92151999j]]
```