cupyx.scipy.signal.iirfilter#

cupyx.scipy.signal.iirfilter(N, Wn, rp=None, rs=None, btype='band', analog=False, ftype='butter', output='ba', fs=None)[source]#

IIR digital and analog filter design given order and critical points.

Design an Nth-order digital or analog filter and return the filter coefficients.

Parameters:

N (int) – The order of the filter.
Wn (array_like) –
A scalar or length-2 sequence giving the critical frequencies.

For digital filters, Wn are in the same units as fs. By default, fs is 2 half-cycles/sample, so these are normalized from 0 to 1, where 1 is the Nyquist frequency. (Wn is thus in half-cycles / sample.)

For analog filters, Wn is an angular frequency (e.g., rad/s).

When Wn is a length-2 sequence, Wn[0] must be less than Wn[1].
rp (float, optional) – For Chebyshev and elliptic filters, provides the maximum ripple in the passband. (dB)
rs (float, optional) – For Chebyshev and elliptic filters, provides the minimum attenuation in the stop band. (dB)
btype ({'bandpass', 'lowpass', 'highpass', 'bandstop'}, optional) – The type of filter. Default is ‘bandpass’.
analog (bool, optional) – When True, return an analog filter, otherwise a digital filter is returned.
ftype (str, optional) –
The type of IIR filter to design:
- Butterworth : ‘butter’
- Chebyshev I : ‘cheby1’
- Chebyshev II : ‘cheby2’
- Cauer/elliptic: ‘ellip’
- Bessel/Thomson: ‘bessel’
output ({'ba', 'zpk', 'sos'}, optional) –
Filter form of the output:
- second-order sections (recommended): ‘sos’
- numerator/denominator (default) : ‘ba’
- pole-zero : ‘zpk’
In general the second-order sections (‘sos’) form is recommended because inferring the coefficients for the numerator/denominator form (‘ba’) suffers from numerical instabilities. For reasons of backward compatibility the default form is the numerator/denominator form (‘ba’), where the ‘b’ and the ‘a’ in ‘ba’ refer to the commonly used names of the coefficients used.

Note: Using the second-order sections form (‘sos’) is sometimes associated with additional computational costs: for data-intense use cases it is therefore recommended to also investigate the numerator/denominator form (‘ba’).
fs (float, optional) – The sampling frequency of the digital system.

Returns:

b, a (ndarray, ndarray) – Numerator (b) and denominator (a) polynomials of the IIR filter. Only returned if output='ba'.
z, p, k (ndarray, ndarray, float) – Zeros, poles, and system gain of the IIR filter transfer function. Only returned if output='zpk'.
sos (ndarray) – Second-order sections representation of the IIR filter. Only returned if output='sos'.