In our robust control course, we learn about uncertainty in the model or in the parameters, so we try to model the worst case of parameter uncertainty on the planet. Planet $G$ suffer from uncertainty in $z$, $p_1$, and $p_2$. how to compute M-Delta representation for the system, I think it some times call it as LFT( Linear Fractional Transformation). Where $M$ represents the input and output and uncertainty, and Delta is a diagonal matrix of $m_1$, $m_2$, $m_3$ as follow
$G(s)=(s+z)/(s+p_1)(s+p_2)$
where:
$p_1=a(1+m_1), \quad|m_1|<1$,
$p_2=b(1+m_2),\quad|m_2|<1$,
$z=c(1+m_3),\quad|m_3|<1$.
where $a, b, c$ are the nominal value of $p_1, p_2$ and $z$ respectively.
