Function HApsi transforms vector u as follows.
\[
HApsi(u) = \left\{
\begin{array}{cc}
u & |u| <= a \\
a \times sign(u) & a <= |u| < b \\
a \frac{c-|u|}{c-b} \times sign(u) & b <= |u| < c \\
0 & |u| >= c
\end{array} \right.
\]
where $a$= ctun *param(1).
$b$= ctun *param(2).
$c$= ctun *param(3).
The default is
$a$= 2*ctun.
$b$= 4*ctun.
$c$= 8*ctun.
It is necessary to have 0 <= a <= b <= c.
Parameter ctun multiplies parameters (a,b,c) of Hampel estimator.