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# scikits.statsmodels.robust.norms.AndrewWave.rho

`AndrewWave.``rho`(z)

  The robust criterion function for Andrew’s wave.

  Parameters: | z : array-like 1d array
  Returns: | array : rho(z) = a*(1-cos(z/a)) for |z| <= a*pi rho(z) = 2*a for |z| > a*pi

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