Frequency filtering for elliptic interface problems with Lagrange multipliers

The solution of the saddle point interface problem arising in hybrid formul ation with the Lagrange multipliers for elliptic problems with nonmatching grids is considered. The preconditioner is constructed using frequency filt ering decompositions of the local Schur complements. The convergence rate o f the resulting iterative process does not depend on the size of the interf ace problem. The approach is applied for the treatment of the local refinem ent procedures and considered as an alternative to the refinement with slav e nodes or full closure of the grid. Numerical experiments on the convergen ce rate are presented.