method
HuberT.
rho
The robust criterion function for Huber’s t.
1d array
rho(z) = .5*z**2 for |z| <= t
rho(z) = |z|*t - .5*t**2 for |z| > t
statsmodels.robust.norms.HuberT.psi_deriv
statsmodels.robust.norms.HuberT.weights