Differential Games for a Mixed ODE-PDE System

Motivated by a vaccination coverage problem, we consider here a zero-sum differential game governed by a differential system consisting of a hyperbolic partial differential equation (PDE) and an ordinary differential equation (ODE). Two players act through their respective controls to influence the evolution of the system with the aim of minimizing their objective functionals F_1 and F_2, under the assumption that F_1 + F_2 = 0. First we prove a well-posedness and a stability result for the differential system, once the control functions are fixed. Then we introduce the concept of nonanticipating strategies for both players, and we consider the associated value functions, which solve two infinite-dimensional Hamilton--Jacobi--Isaacs equations in the viscosity sense.