# scipy.signal.symiirorder2

scipy.signal.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

  Parameters:
    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.

  Returns:
    output ndarray

      The filtered signal.