statsmodels.robust.norms.AndrewWave.psi

AndrewWave.psi(z)

The psi function for Andrew’s wave

The analytic derivative of rho

Parameters:z (array-like) – 1d array Returns:psi – psi(z) = sin(z/a) for |z| <= a*pi

psi(z) = 0 for |z| > a*pi

Return type:array