sosfilt_zi(sos)
Compute an initial state zi for the sosfilt function that corresponds to the steady state of the step response.
A typical use of this function is to set the initial state so that the output of the filter starts at the same value as the first element of the signal to be filtered.
Array of second-order filter coefficients, must have shape (n_sections, 6). See sosfilt for the SOS filter format specification.
Initial conditions suitable for use with sosfilt, shape (n_sections, 2).
Construct initial conditions for sosfilt for step response steady-state.
import numpy as np
from scipy import signal
import matplotlib.pyplot as plt
sos = signal.butter(9, 0.125, output='sos')
zi = signal.sosfilt_zi(sos)
x = (np.arange(250) < 100).astype(int)
f1 = signal.sosfilt(sos, x)
f2, zo = signal.sosfilt(sos, x, zi=zi)
plt.plot(x, 'k--', label='x')
plt.plot(f1, 'b', alpha=0.5, linewidth=2, label='filtered')
plt.plot(f2, 'g', alpha=0.25, linewidth=4, label='filtered with zi')
plt.legend(loc='best')
plt.show()
The following pages refer to to this document either explicitly or contain code examples using this.
scipy.signal._signaltools:sosfilt
scipy.signal._signaltools:sosfiltfilt
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