  The formalism of subdynamics is extended to the functional approach of
quantum systems, and used for the Friedrichs model, in which diagonal
singularities in states and observables are included. We compute in this
approach the generalized eigenvectors and eigenvalues of the Liouvulle-Von
Newmann operator, using an iterative scheme. As complex generalized eigenvalues
are obtained, the decay rates of unstable modes are included in the spectral
decomposition.
