Design of interface modules for flexible coupling of finite element codes with solvers of linear equations

This paper presents the design of flexible interfaces between finite element (FE) codes and solvers of linear equations. The main goal of the design is to allow for coupling FE codes that use different formulations (linear, non-linear, time dependent, stationary, scalar, vector) and different approximation techniques (different element types, different approximation spaces – linear, higher order, continuous, discontinuous, h- and hp-adaptive) with solvers of linear equations that use different storage formats for sparse system matrices and different solution strategies (such as, e.g., reordering of degrees of freedom (DOFs), multigrid solution or preconditioning for iterative solvers, frontal and multi-frontal strategies for direct solvers). Suitable data structures associated with the design are presented and examples of algorithms related to the interface between the FEM codes and linear solvers, together with their execution time and performance estimates, are described.