Tukey's Biwelght. A popular (psi) function for robust regression is Tukey's biweight, where [ psi(z)= begin{cases}zleft[1-(z / a)^{2} ight]^{2}, & |z| leq a 0,

Tukey's Biwelght. A popular \(\psi\) function for robust regression is Tukey's biweight, where

\[
\psi(z)= \begin{cases}z\left[1-(z / a)^{2}\right]^{2}, & |z| \leq a \\ 0, & |z|>a\end{cases}
\]

with \(a=5\). Sketch the \(\psi\) function for \(a=5\) and discuss its behavior. Do you think that Tukey's biweight would give results similar to Andrews' wave function?