Mixed approximation of a population diffusion equation

A numerical method is proposed to approximate the solution of a nonlinear and nonlocal system of integro-differential equations describing age-dependent population dynamics with spatial diffusion. A finite difference method along the characteristic age-time direction combined with mixed finite elements in the spatial variable is used for the approximation. Optimal order error estimates are derived for the relevant variables. Using nonnegativity of the discrete solution, a stability of the method is also proved.