For a, b > 0, if \(\mathrm{P}=\left[\begin{array}{cc}0 & -\mathrm{a} \\ 2 \mathrm{a} & \mathrm{b}\end{array}\right]\) and \(\mathrm{Q}=\left[\begin{array}{cc}\mathrm{b} & \mathrm{a} \\ -\mathrm{b} & 0\end{array}\right]\) are two matrices such that \(P Q=\left[\begin{array}{ll}2 & 0 \\ 3 & 8\end{array}\right]\), then the value of (a + b)^ab is: