Matemática Error analysis Finite element method Ciencias Exactas Finite elements Divergence operator Interpolation Approximation theory Convection-diffusion Eigenvalues and eigenfunctions Graded meshes Green function Problem solving Stokes equations Anisotropic elements Anisotropic finite elements Boundary conditions Calderón-Zygmund theory Eigenvalue problems Eigenvalues Error estimates Finite Element Mixed finite elements Numerical methods Poincaré inequalities Reissner-Mindlin Singular integrals Superconvergence Weighted Sobolev spaces A POSTERIORI ERROR ESTIMATES