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# scikits.statsmodels.robust.norms.TukeyBiweight.rho

`TukeyBiweight.``rho`(z)

  The robust criterion function for Tukey’s biweight estimator

  Parameters: | z : array-like 1d array
  Returns: | array : rho(z) = -(1 - (z/c)**2)**3 * c**2/6. for |z| <= R rho(z) = 0 for |z| > R

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