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# scipy.fftpack.cs_diff

`scipy.fftpack.``cs_diff`(x, a, b, period=None, _cache={})

  cs_diff(x, a, b, period=2*pi) -> y

  Return (a,b)-cosh/sinh pseudo-derivative of a periodic sequence x.

  If x_j and y_j are Fourier coefficients of periodic functions x and y, respectively, then

  > y_j = -sqrt(-1)*cosh(j*a*2*pi/period)/sinh(j*b*2*pi/period) * x_j y_0 = 0

  Input:
    a,b
      Defines the parameters of the cosh/sinh pseudo-differential operator.
    period
      The period of the sequence. Default period is 2*pi.
  Notes:
    For even len(x), the Nyquist mode of x is taken zero.

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