We introduce an alternative nonperturbative method to the master equation f
ormalism of describing the evolution of coupled linear systems. The method
utilizes the spectral distribution of the normal modes of the complete syst
em to calculate the evolution of the dynamical variables. The dynamical evo
lution of the Wigner function for a Schrodinger cat state in a damped cavit
y is considered as example. (C) 2000 Elsevier Science B.V. All rights reser
ved.