Finite element approximation of the fast diffusion and the porous medium equations

The fast diffusion equation u(t) =Delta(vertical bar u vertical bar(m- 1)u)(0 < m < 1) and the porous medium equation (1 < m < infinity) are studied in a parabolic cylinder Omega x (0, T). A fully discrete Galerkin approximation is considered using C-0-piecewise linear finite elements in space and the backward Euler time discretization. A priori error estimates in quasi norms and rates of convergence are proved.