On an Additive Schwarz Preconditioner for the Crouzeix-Raviart Mortar Finite Element

We consider an additive Schwarz preconditioner for the algebraic system resulting from the discretization of second order elliptic equations with discontinuous coefficients, using the lowest order Crouzeix-Raviart element on nonmatching meshes. The overall discretization is based on the mortar technique for coupling nonmatching meshes. A convergence analysis of the preconditioner has recently been given in Rahman et al. [2003]. In this paper, we give a matrix formulation of the preconditioner, and discuss some of its numerical properties.