A Coupled Multigrid Method for Nonconforming Finite Element Discretizations of the 2D-Stokes Equation

This paper investigates a multigrid method for the solution of the saddle point formulation of the discrete Stokes equation obtained with inf–sup stable nonconforming finite elements of lowest order. A smoother proposed by Braess and Sarazin (1997) is used and L ²-projection as well as simple averaging are considered as prolongation. The W-cycle convergence in the L ²-norm of the velocity with a rate independently of the level and linearly decreasing with increasing number of smoothing steps is proven. Numerical tests confirm the theoretically predicted results. Received January 19, 1999; revised September 13, 1999