## Polytopal meshes and complex porous media flows

Main results: general polytopal meshes; easy-to-implement and fast-to-run estimates given by a simple matrix–vector multiplication; works for any lowest-order locally conservative method; guaranteed upper bound on the total error; distinction of different error components (spatial discretization, temporal discretization, linearization, algebraic solver); unsteady nonlinear coupled degenerate problems (multiphase multicomponent flows in…