Parallel Newton--Krylov BDDC and FETI-DP Deluxe Solvers for Implicit Time discretizations of the Cardiac Bidomain Equations

Two novel parallel Newton--Krylov balancing domain decomposition by constraints (BDDC) and dual-primal finite element tearing and interconnecting (FETI-DP) solvers with deluxe scaling are constructed, analyzed, and tested numerically for implicit time discretizations of the three-dimensional bidomain system of equations. This model represents the most advanced mathematical description of the cardiac bioelectrical activity, and it consists of a degenerate system of two nonlinear reaction-diffusion partial differential equations (PDEs), coupled with a stiff system of ordinary differential equations (ODEs). A finite element discretization in space and a segregated implicit discretization in time, based on decoupling the PDEs from the ODEs, yields at each time step the solution of a nonlinear algebraic system. The Jacobian linear system at each Newton iteration is solved by a Krylov method, accelerated by BDDC or FETI-DP preconditioners, both augmented with the recently introduced deluxe scaling of the dual variables. A polylogarithmic convergence rate bound is proven for the resulting parallel Bidomain solvers. Extensive numerical experiments on Linux clusters up to two thousand processors confirm the theoretical estimates, showing that the proposed parallel solvers are scalable and quasi-optimal.