A null space algorithm for mixed finite element approximations of Darcy's equation.

A null space algorithm is considered to solve the augmented system produced by the mixed niteelement approximation of Darcy's Law. The method is based on the combination of an orthogonal factorization technique for sparse matrices with an iterative Krylov solver. The computational eciency of the method relies on a suitable stopping criterion for the iterative solver. We experimentally investigate its performance on a realistic set of selected application problems.