`scipy.signal._spline_filters:symiirorder2`

Signature

def symiirorder2(input, r, omega, precision = -1.0)

Implement a smoothing IIR filter with mirror-symmetric boundary conditions using a cascade of second-order sections.

The second section uses a reversed sequence. This implements the following transfer function

                         cs^2
H(z) = ---------------------------------------
       (1 - a2/z - a3/z^2) (1 - a2 z - a3 z^2 )

where

a2 = 2 * r * cos(omega)
a3 = - r ** 2
cs = 1 - 2 * r * cos(omega) + r ** 2

input : ndarray: The input signal.
r, omega : float: Parameters in the transfer function.
precision : float: Specifies the precision for calculating initial conditions of the recursive filter based on mirror-symmetric input.