Subharmonic solutions for nonautonomous sublinear first order Hamiltonian systems

In this paper, the existence of subharmonic solutions for a class of non-autonomous first-order Hamiltonian systems is investigated. We also study the minimality of periods for such solutions. Our results which extend and improve many previous results will be illustrated by specific examples. Our main tools are the minimax methods in critical point theory and the least action principle. {\bf Key words.} Hamiltonian systems. Critical point theory. Least action principle. Subharmonic solutions.