statsmodels.robust.norms.TukeyBiweight.psi#
- TukeyBiweight.psi(z)[source]#
The psi function for Tukey’s biweight estimator
The analytic derivative of rho
- Parameters:
- zarray_like
1d array
- Returns:
- psi
ndarray psi(z) = z*(1 - (z/c)**2)**2 for |z| <= c
psi(z) = 0 for |z| > c
- psi