statsmodels.robust.norms.TukeyBiweight.psi

TukeyBiweight.psi(z)[source]

The psi function for Tukey’s biweight estimator

The analytic derivative of rho

Parameters:z (array-like) – 1d array
Returns:psi – psi(z) = z*(1 - (z/c)**2)**2 for |z| <= R

psi(z) = 0 for |z| > R
Return type:array