Many nonclassical problems in
the calculus of variations, arising for example from control theory, correspond in a
sense to “Hamiltonian” functions which are not everywhere differentiable, but are
convex in one vector argument and concave in the other. Optimal arcs in such
problems satisfy generalized ordinary differential equations, defined in terms of
subgradients of the “Hamiltonian.” Such equations are treated in this paper by
convexity methods. An existence theorem is derived from a result of Castaing, and
various properties of solutions are established.