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# scikits.statsmodels.robust.norms.Hampel.rho

`Hampel.``rho`(z)

  The robust criterion function for Hampel’s estimator

  Parameters: | z : array-like 1d array
  Returns: | array : rho(z) = (1/2.)*z**2 for |z| <= a rho(z) = a*|z| - 1/2.*a**2 for a < |z| <= b rho(z) = a*(c*|z|-(1/2.)*z**2)/(c-b) for b < |z| <= c rho(z) = a*(b + c - a) for |z| > c

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