How to put complex into a numpy's array?

Question

>>> import numpy as np
>>> A = np.zeros((3,3))
>>> A[0,0] = 9
>>> A
array([[ 9.,  0.,  0.],
       [ 0.,  0.,  0.],
       [ 0.,  0.,  0.]])
>>> A[0,1] = 1+2j
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't convert complex to float
>>> A[0,1] = np.complex(1, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't convert complex to float

According to my example code. i tried to put complex number into the numpy's array but it didn't work. May be i miss some basic thing.

Answer 1

If you want to create an array containing complex values, you need to specify a complex type to numpy:

>>> A = np.zeros((3,3), dtype=complex)

>>> print A
[[ 0.+0.j  0.+0.j  0.+0.j]
 [ 0.+0.j  0.+0.j  0.+0.j]
 [ 0.+0.j  0.+0.j  0.+0.j]]

>>> A[0,0] = 1. + 2.j

>>> print A
[[ 1.+2.j  0.+0.j  0.+0.j]
 [ 0.+0.j  0.+0.j  0.+0.j]
 [ 0.+0.j  0.+0.j  0.+0.j]]

Answer 2

You need to convert the array's type.

Example:

>>> from numpy import array, dtype
>>> A = array([1, 2, 3])
>>> A[0] = 1+2j
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: can't convert complex to long
>>> B = A.astype(dtype("complex128"))
>>> B[0] = 1+2j
>>> B
array([ 1.+2.j,  2.+0.j,  3.+0.j])
>>>