[P,C,X] = evalsystempriors(M,S)
M [ model ] - Model object on which current parameterisation the system priors will be evaluated.
S [ systempriors ] - System priors objects.
P [ numeric ] - Minus log of system prior density.
C [ numeric ] - Contributions of individual prios to the overall system prior density.
X [ numeric ] - Value of each system property for which a prior has been defined in the system priors object, S.