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# scipy.signal.iirfilter

`scipy.signal.``iirfilter`(N, Wn, rp=None, rs=None, btype='band', analog=0, ftype='butter', output='ba')

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

  Design an Nth order lowpass digital or analog filter and return the filter coefficients in (B,A) (numerator, denominator) or (Z,P,K) form.

  Parameters : | N : int The order of the filter. Wn : array_like A scalar or length-2 sequence giving the critical frequencies. rp : float, optional For Chebyshev and elliptic filters provides the maximum ripple in the passband. rs : float, optional For chebyshev and elliptic filters provides the minimum attenuation in the stop band. btype : str, optional The type of filter (lowpass, highpass, bandpass, bandstop). Default is bandpass. analog : int, optional Non-zero to return an analog filter, otherwise a digital filter is returned. ftype : str, optional The type of IIR filter to design: elliptic : ‘ellip’ Butterworth : ‘butter’, Chebyshev I : ‘cheby1’, Chebyshev II: ‘cheby2’, Bessel : ‘bessel’ output : [‘ba’, ‘zpk’], optional Type of output: numerator/denominator (‘ba’) or pole-zero (‘zpk’). Default is ‘ba’.

  See also

  `butterord`, `cheb1ord`, `cheb2ord`, `ellipord`

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