Slow Initial Convergence of GMRES for SUPG Discretized Convection‐Diffusion Problems

When GMRES [6] is applied to streamline upwind Petrov Galerkin (SUPG) discretized convection‐diffusion problems, its residual norms typically exhibit an initial period of slow convergence. For a model problem we offer a quantitative explanation of this behavior and relate it to the boundary conditions.