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# scipy.signal.symiirorder2

`scipy.signal.``symiirorder2`()

  symiirorder2(input, r, omega {, precision}) -> output

  Description:

  > 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

  Inputs:

  > input – the input signal. r, omega – parameters in the transfer function. precision – specifies the precision for calculating initial conditions

  > > of the recursive filter based on mirror-symmetric input.

  Output:

  > output – filtered signal.

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