Remhos

Remhos (REMap High-Order Solver) is a CEED miniapp that performs monotonic and conservative high-order discontinuous field interpolation (remap) using DG advection-based spatial discretization and explicit high-order time-stepping.

Lawrence Livermore National Laboratory

ECP

BLAST

DG Advection

high-order, finite elements, remap, advection, transport

C++

https://github.com/CEED/Remhos

1.0

remhos

The problem that Remhos is solving is formulated as a time-dependent system of ordinary differential equations (ODEs) for the unknown coefficients of a high-order finite element (FE) function. The left-hand side of this system is controlled by a mass matrix, while the right-hand side is constructed from a advection matrix. Remhos supports two execution modes, namely, transport and remap, which result in slightly different algebraic operators. The main difference between the two modes is that in the case of remap, the mass and advection matrices change in time, while they are constant for the transport case. Remhos supports two options for deriving and solving the ODE system, namely the full assembly and the partial assembly methods. Partial assembly is the main algorithm of interest for high orders. For low orders (e.g. 2nd order in 3D), both algorithms are of interest. The full assembly option relies on constructing and utilizing global mass and advection matrices stored in compressed sparse row (CSR) format. In contrast, the partial assembly option defines only the local action of those matrices, which is then used to perform all necessary operations. As the local action is defined by utilizing the tensor structure of the finite element spaces, the amount of data storage, memory transfers, and FLOPs are lower (especially for higher orders). Other computational motives in Remhos include the following: - Support for unstructured meshes, in 2D and 3D, with quadrilateral and hexahedral elements. Serial and parallel mesh refinement options can be set via a command-line flag. - Explicit time-stepping loop with a variety of time integrator options. Remhos supports Runge-Kutta ODE solvers of orders 1, 2, 3, 4 and 6. - Discontinuous high-order finite element discretization spaces of runtime-specified order. - Moving (high-order) meshes. - Mass operator that is local per each zone. It is inverted by iterative or exact methods at each time step. This operator is constant in time (transport mode) or changing in time (remap mode). Options for full or partial assembly. - Advection operator that couples neighboring zones. It is applied once at each time step. This operator is constant in time (transport mode) or changing in time (remap mode). Options for full or partial assembly. - Domain-decomposed MPI parallelism. - Optional in-situ visualization with GLVis and data output for visualization and data analysis with VisIt.