statsmodels.robust.norms.AndrewWave.psi#
- AndrewWave.psi(z)[source]#
The psi function for Andrew’s wave
The analytic derivative of rho.
\[\begin{split}\psi(z) = \begin{cases} a \sin(z/a) & \text{for } |z| \le a\pi \\ 0 & \text{for } |z| > a\pi \end{cases}\end{split}\]- Parameters:
- zarray_like
1d array
- Returns:
- psi
ndarray The value of the psi function.
- psi