  We investigate how the concepts of optimal control of measurables of a system
with a time dependent Hamiltonian may be mixed with the level set technique to
keep the desired entity invariant. We derive sets of equations for this purpose
and also algorithms for numerical use. The notion of constancy of measurables
in this context is also examined to make the techniques more useful in
real-life situation where some variability of the measurable may be tolerable.
