$\rho$ ($\psi$) function which is considered is standardized
using intervals 0---(2/3)c , (2/3)c---c, >c.
$\rho$ function is
\[
OPTrho(u)= \left\{
\begin{array}{lr}
1.3846 \left(\frac{u}{c}\right)^2 & |\frac{u}{c}| \leq \frac{2}{3} \\
0.5514-2.6917 \left(\frac{u}{c}\right)^2 +10.7668\left(\frac{u}{c}\right)^4-11.6640\left(\frac{u}{c}\right)^6+4.0375\left(\frac{u}{c}\right)^8 & \qquad \frac{2}{3} \leq |\frac{u}{c}|\leq 1 \\
1 & |\frac{u}{c}|>1 \\
\end{array}
\right.
\]