CH02_SEC02_1_DFT.ipynb

Kernel: Python 3

import numpy as np
import matplotlib.pyplot as plt
plt.rcParams['figure.figsize'] = [8, 8]
plt.rcParams.update({'font.size': 18})

n = 256
w = np.exp(-1j * 2 * np.pi / n)

DFT = np.zeros((n,n))

# Slow
for i in range(n):
    for k in range(n):
        DFT[i,k] = w**(i*k)
        
DFT = np.real(DFT)
        
plt.imshow(DFT)
plt.show()

C:\ProgramData\Anaconda3\lib\site-packages\ipykernel_launcher.py:6: ComplexWarning: Casting complex values to real discards the imaginary part
  

# Fast
J,K = np.meshgrid(np.arange(n),np.arange(n))
DFT = np.power(w,J*K)
DFT = np.real(DFT)
       
plt.imshow(DFT)
plt.show()