Summary. The simulation of flow in porous media is a computationally demanding task. Thermodynamical equilibrium calculations and complex, heterogeneous geological structures normally gives a multiphysics/multidomain problem to solve. Thus, efficient solution methods are needed. The research simulator Athena is a 3D, multiphase, multicomponent, porous media flow simulator. A parallel version of the simulator was developed based on a non-overlapping domain decomposition strategy, where the domains are defined a-priori from e.g. geological data. Selected domains are refined with locally matching grids, giving a globally non-matching, unstructured grid. In addition to the space domain, novel algorithms for parallel processing in time based on a predictor-corrector strategy has been successfully implemented. We discuss how the domain decomposition framework can be used to include different physical and numerical models in selected sub-domains. Also we comment on how the two-level solver relates to multiphase upscaling techniques. Adding communication functionality enables the original serial version to run on each sub-domain in parallel. Motivated by the need for larger time steps, an implicit formulation of the mass transport equations has been formulated and implemented in the existing parallel framework. Further, as the Message Passing Interface (MPI) is used for communication, the simulator is highly portable. Through benchmark experiments, we test the new formulation on platforms ranging from commercial super-computers to heterogeneous networks of workstations. 1

by Lie-Quan Lee Generic programming is an important paradigm for software development, with an emphasis on reusability and performance, qualities that would seemingly make this para-digm especially suited for application to scientific computing. We apply generic pro-gramming to the development of a message passing framework (the Generic Message Passing library) for parallel computing in hybrid execution architectures (i.e., those hav-ing both shared and distributed memory). Although GMP supports both shared-memory and distributed-memory execution, it explicitly separates its programming and execution models, presenting a uniform message-based programming interface to enable source-code portability of parallel programs. At the same time, the implementation of GMP fully exploits the architectural characteristics of its execution target for maximum run-time performance. GMP is specifically designed to seamlessly integrate with modern generic C++ libraries such as the C++ Standard Library. C++ objects with complex data