This research monograph deals with optimal periodic control problems for
systems governed by ordinary and functional differential equations of
retarded type. Particular attention is given to the problem of local
properness, i.e. whether system performance can be improved by
introducing periodic motions. Using either Ekeland's Variational
Principle or optimization theory in Banach spaces, necessary optimality
conditions are proved. In particular, complete proofs of second-order
conditions are included and the result is used for various versions of
the optimal periodic control problem. Furthermore a scenario for local
properness (related to Hopf bifurcation) is drawn up, giving hints as to
where to look for optimal periodic solutions. The book provides
mathematically rigorous proofs for results which are potentially of
importance in chemical engineering and aerospace engineering.