`scipy.signal._czt:czt_points`

Signature

def czt_points(m, w = None, a = (1+0j))

Return the points at which the chirp z-transform is computed.

m : int: The number of points desired.
w : complex, optional: The ratio between points in each step. Defaults to equally spaced points around the entire unit circle.
a : complex, optional: The starting point in the complex plane. Default is 1+0j.

out : ndarray: The points in the Z plane at which CZT samples the z-transform, when called with arguments m, w, and a, as complex numbers.

Plot the points of a 16-point FFT:

import numpy as np
from scipy.signal import czt_points
points = czt_points(16)
import matplotlib.pyplot as plt

✓

plt.plot(points.real, points.imag, 'o')
plt.gca().add_patch(plt.Circle((0,0), radius=1, fill=False, alpha=.3))
plt.axis('equal')

✗

(np.float64(-1.1), np.float64(1.1), np.float64(-1.1), np.float64(1.1))

plt.show()

✓

and a 91-point logarithmic spiral that crosses the unit circle:

m, w, a = 91, 0.995*np.exp(-1j*np.pi*.05), 0.8*np.exp(1j*np.pi/6)
points = czt_points(m, w, a)

✓

plt.plot(points.real, points.imag, 'o')
plt.gca().add_patch(plt.Circle((0,0), radius=1, fill=False, alpha=.3))
plt.axis('equal')

✗

(np.float64(-1.1750277396780497), np.float64(1.287130895350953), np.float64(-1.2354276356015903), np.float64(1.3532932245402811))

plt.show()

✓