Green's function for the steady state of a periodically excited circuit

The problem of finding the steady-state solution x(t) of the equation P^{^}x(t) = Q^{^}f(t) is studied, where f(t) is a periodical excitation, and P^{^}and Q^{^}are ordinary linear differential operators with constant coefficients For this purpose, a Green's function is constructed, which is the solution of the problem when the excitation f(t) consists of periodically applied pulses. This Green's function is then used in a convolution integral to find the steady-state solution for any periodical f(t).