`scipy.signal._signaltools:sosfilt_zi`

source: /scipy/signal/_signaltools.py :4451

Signature

def sosfilt_zi ( sos )

Summary

Construct initial conditions for sosfilt for step response steady-state.

Extended Summary

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.

Parameters

sos : array_like: Array of second-order filter coefficients, must have shape (n_sections, 6). See sosfilt for the SOS filter format specification.

Returns

zi : ndarray: Initial conditions suitable for use with sosfilt, shape (n_sections, 2).

Notes

Array API Standard Support

sosfilt_zi has experimental support for Python Array API Standard compatible backends in addition to NumPy. Please consider testing these features by setting an environment variable SCIPY_ARRAY_API=1 and providing CuPy, PyTorch, JAX, or Dask arrays as array arguments. The following combinations of backend and device (or other capability) are supported.

====================  ====================  ====================
Library               CPU                   GPU
====================  ====================  ====================
NumPy                 ✅                     n/a                 
CuPy                  n/a                   ✅                   
PyTorch               ✅                     ✅                   
JAX                   ✅                     ✅                   
Dask                  ✅                     n/a                 
====================  ====================  ====================

See dev-arrayapi for more information.

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()

✓

`scipy.signal._signaltools:sosfilt_zi`

Signature

Summary

Extended Summary

Parameters

Returns

Notes

Examples

See also

Aliases

Referenced by

This package