Classical fields as constrained systems

Classical fields are treated as singular systems in (n + 4)-dimensional space formed by fields φi, i = 1,2, ..., n, and xμ. Integrability conditions of canonical equations are determined and plane-wave solutions of free fields are obtained. Application of the formalism to the Lagrangian of a charged particle interacting with electromagnetic field leads to the Lienard-Wiechert potentials