Using MPI and OpenMP

Domain Decomposition: MeshBlock

For parallel simulations with MPI, the computing domain is decomposed into small units. In Athena++, this decomposition unit is called MeshBlock, and all the MeshBlock must have the same logical size (i.e., the number of cells). These MeshBlocks are stored on a tree structure, and have unique integer IDs numbered by Z-ordering.

The MeshBlock size is specified by <meshblock> parameters in an input file. The following example is decomposing a Mesh with 256^3 into MeshBlocks with 64^3 cells, resulting in 64 MeshBlocks. Obviously, the size of Mesh must be divisible by MeshBlocks.

<mesh>
nx1     =    256
...
nx2     =    256
...
nx3     =    256
...
<meshblock>
nx1     =    64
nx2     =    64
nx3     =    64

MPI Parallelization

OpenMP Parallelization