The optimal control problem for a nonlinear elliptic population system is considered.First, under certain hypotheses, the existence and uniqueness of coexistence state solutions are shown. Then the existence of the optimal control is given and the optimality system is established.
This paper considers the exponential decay of the solution to a damped semilinear wave equation with variable coefficients in the principal part by Riemannian multiplier method. A differential geometric condition that ensures the exponential decay is obtained.
The internal control problem is considered, based on the linear displacement equations of shallow shell. It is shown, with some checkable geometric conditions on control region, that the undergoing shallow shell is exactly controllable by using Hilbert uniqueness method （HUM）, piecewise multiplier method and Riemannian geometry method. Then some examples are given to show the assumed geometric conditions.
