scipy.signal.
sosfilt_zi#
- scipy.signal.sosfilt_zi(sos)[source]#
- Construct initial conditions for sosfilt for step response steady-state. - Compute an initial state zi for the - sosfiltfunction 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. - Parameters:
- sosarray_like
- Array of second-order filter coefficients, must have shape - (n_sections, 6). See- sosfiltfor the SOS filter format specification.
 
- Returns:
- zindarray
- Initial conditions suitable for use with - sosfilt, shape- (n_sections, 2).
 
 - Notes - Added in version 0.16.0. - Examples - Filter a rectangular pulse that begins at time 0, with and without the use of the zi argument of - scipy.signal.sosfilt.- >>> 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() 