Numpy array assignment with complex values gets error: "ComplexWarning: Casting complex values to real discards the imaginary part"

Question

I'm trying to do these kind of operations:

width = 23
alpha_i = np.array([1.84704762, 1.7878235 , 1.72701305, 1.66501652, 1.60228591,
   1.53930674, 1.47657613, 1.41457961, 1.35376915, 1.29454503])

w_s_i = (wc / c) * d * np.cos(alpha_i) 
ws_idx = np.zeros((width, 1)) # vettore che contiene "width" elementi spaziati di 1
ii = 0
for i in range(np.int(np.floor(width / 2)),-np.int(np.floor(width / 2))-1,-1):
   ws_idx[ii,:] =  i
   ii = ii + 1


# eq.(7)
steer_vecs = np.zeros((width, alpha_i.shape[0]));
   for i in range(0,10):
   steer_vecs[:, i] = np.squeeze(np.exp(1j * np.multiply(ws_idx ,w_s_i[i])),axis=1)

But I don't know why at the end of the last for loop the imaginary part get discarded.. I get the following error:

ComplexWarning: Casting complex values to real discards the imaginary part

Any suggestions? thanks!

Stef · Accepted Answer · 2021-01-24 16:13:08Z

1

The left hand side steer_vecs[:, i] is an array of type float64, the default type. So if you try to assign complex values to a float array you get the warning.

So you need to declare steer_vecs as a complex array:

steer_vecs = np.zeros((width, alpha_i.shape[0]), dtype=np.complex)

answered Jan 24, 2021 at 16:13

Stef

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