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# scikits.statsmodels.robust.norms.TrimmedMean.psi

`TrimmedMean.``psi`(z)

  The psi function for least trimmed mean

  The analytic derivative of rho

  Parameters: | z : array-like 1d array
  Returns: | array : psi(z) = z for |z| <= c psi(z) = 0 for |z| > c

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