The impact of enabling multiple subdomains per MPI process in the TFETI domain decomposition method

The paper deals with handling multiple subdomains per computational core in the PERMON toolbox, namely in the PermonFLLOP module, to fully exploit the potential of the Total Finite Element Tearing and Interconnecting (TFETI) domain decomposition method (DDM). Most authors researching FETI methods present weak parallel scalability with one subdomain assigned to each computational core, and call it just parallel scalability. Here we present an extension showing the data of more than one subdomain being held by each MPI process. Numerical experiments demonstrate the theoretically supported fact that for the given problem size and number of processors, the increased number of subdomains leads to better conditioning of the system operator, and hence faster convergence. Moreover, numerical, memory, strong parallel, and weak parallel scalability is reported, and optimal numbers of subdomains per core are examined. Finally, new PETSc matrix types dealing with the aforementioned extension are introduced.