I have a python code where it shows complexwarning while compiling. Can anyone resolve this?

Question

I am having problem with the following python code:

import numpy as np
import numpy.linalg as LA
import math
import cmath
from decimal import *

No = 1000
n = 3
mult = 1

file = open("diff_%d_%d.txt" %(n, mult), "w")

for l in range (0, No): 
    product = np.identity(n)
    for K in range (1,mult+1):
        A = np.random.standard_normal(size=(n,n))
        product = np.dot(product,A)
    norm = LA.norm(product)
    Normalized_Matrix = product/float(norm) 

    eigen_value, eigen_vector = LA.eig(Normalized_Matrix)

    if ((eigen_value[0].imag == 0) & (eigen_value[1].imag != 0) & (eigen_value[2].imag != 0)):
        file.write("%f\n" % (eigen_value[0]))
    if ((eigen_value[0].imag != 0) & (eigen_value[1].imag == 0) & (eigen_value[2].imag != 0)):
        file.write("%f\n" % (eigen_value[1]))
    if ((eigen_value[0].imag != 0) & (eigen_value[1].imag != 0) & (eigen_value[2].imag == 0)):
        file.write("%f\n" % (eigen_value[2]))

file.close()

After running this code, I have the error that shows: ComplexWarning: Casting complex values to real discards the imaginary part file.write("%f\n" % (eigen_value[2]))

Can anyone help me resolving this problem?

Answer 1

The message, ComplexWarning: Casting complex..., you are getting is not an error but a warning. If you got no other messages, likely your code ran through. However you may not be getting the results you are expecting.

The warning indicates that you are converting complex values into real. Doing this discards the imaginary component. The function, LA.eig(), returns complex results. When you write out the results with file.write("%f\n" % eigen_value[2]), you are converting to a float (real number).

If the imaginary component is important, you can do something like: file.write("%f + j%f\n" % (eigen_value[2].real, eigen_value[2].imag))