Flux Jacobian for flux splitting
 

I am doing a quasi-1D euler solver and implementing flux vector splitting.
So I need the fluxes A, |A|
where |A|=A^+ - A^-
and
$ A^{+/-)=P \Lamda^{+/-} P^{-1} $

In short, I can get |A| by doing the inversions, etc above. Alternatively, does anybody have a reference where I can get |A|?