method
TukeyBiweight.
rho
The robust criterion function for Tukey’s biweight estimator
1d array
rho(z) = -(1 - (z/c)**2)**3 * c**2/6. for |z| <= R
rho(z) = 0 for |z| > R
statsmodels.robust.norms.TukeyBiweight.psi_deriv
statsmodels.robust.norms.TukeyBiweight.weights