Preconditioning the mortar method by substructuring: the high order case

We analyze a class of preconditioners for the mortar method, based on substructuring. After splitting in a suitable way the degrees of freedom in interior, edge and vertex, we study the performance of a block Jacobi type preconditioner for which the condition number of the preconditioned matrix only grows polylogarithmically. Unlike the previous work by Achdou, Maday and Widlund [1], which is restricted to the case of first order finite element, this paper relies on abstract assumptions and therefore applies to finite element of any order. Moreover, the use of a suitable coarse preconditioner (whose effect we analyze) makes this technique more efficient.