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Time optimal problems with Dirichlet boundary controls
We consider time optimal control problems governed by
semilinear parabolic equations with Dirichlet
boundary controls in the presence of a target state constraint. To establish optimality conditions
for the terminal time $T$, we define a new Hamiltonian functional. Due to regularity results
for the state and the adjoint state variables, this Hamiltonian
belongs to $L_{l o c}^r(0,T)$ for some $r>1$. By proving that it satisfies a differential
equation corresponding to an optimality condition for $T$, we deduce that it belongs to
$W^{1,1}(0,T)$. This result answers to the question: how to define Hamiltonian
functionals for infinite dimensional problems with variable endpoints
(see [10], p. 282 and p. 595).