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