Updated README.md that MPI runs are production-ready.

README.md

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 ## Standalone Module
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+# Astaroth - A Multi-GPU Library for Generic Stencil Computations {#mainpage}
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+[Specification](doc/Astaroth_API_specification_and_user_manual/API_specification_and_user_manual.md) | [Contributing](CONTRIBUTING.md) | [Licence](LICENCE.md) | [Repository](https://bitbucket.org/jpekkila/astaroth) | [Issue Tracker](https://bitbucket.org/jpekkila/astaroth/issues?status=new&status=open) | [Wiki](https://bitbucket.org/jpekkila/astaroth/wiki/Home)
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+Astaroth is a multi-GPU library for three-dimensional stencil computations. It is designed especially for performing high-order stencil
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+computations in structured grids, where several coupled fields are updated each time step. Astaroth consists of a multi-GPU and single-GPU
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+APIs and provides a domain-specific language for translating high-level descriptions of stencil computations into efficient GPU code. This
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+makes Astaroth especially suitable for multiphysics simulations.
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+​
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+Astaroth is licenced under the terms of the GNU General Public Licence, version 3, or later
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+(see [LICENCE.txt](LICENCE.md)). For contributing guidelines,
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+see [Contributing](CONTRIBUTING.md).
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+​
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+## System Requirements
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+* An NVIDIA GPU with support for compute capability 3.0 or higher (Kepler architecture or newer)
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+​
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+## Dependencies
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+Relative recent versions of
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+​
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+`gcc cmake cuda flex bison`.
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+​
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+## Building
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+​
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+In the base directory, run
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+​
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+1. `mkdir build`
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+2. `cd build`
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+3. `cmake ..`
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+4. `make -j`
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+​
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+> **Optional:** Documentation can be generated by running `doxygen` in the base directory. Generated documentation can be found in `doc/doxygen`.
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+​
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+> **Tip:**  The library is configured by passing [options](#markdown-header-cmake-options) to CMake with `-D[option]=[ON|OFF]`. For example, double precision can be enabled by calling `cmake -DBUILD_DOUBLE_PRECISION=ON ..`. See [CMakeLists.txt](https://bitbucket.org/jpekkila/astaroth/src/master/CMakeLists.txt) for an up-to-date list of options.
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+​
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+> **Note:** CMake will inform you if there are missing dependencies.
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+​
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+## CMake Options
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+​
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+| Option | Description | Default |
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+|--------|-------------|---------|
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+| CMAKE_BUILD_TYPE | Selects the build type. Possible values: Debug, Release, RelWithDebInfo, MinSizeRel. See (CMake documentation)[https://cmake.org/cmake/help/latest/variable/CMAKE_BUILD_TYPE.html] for more details. | Release |
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+| CUDA_ARCHITECTURES | Selects CUDA architecture support. Multiple architectures delimited by `;`. See (CMake documentation)[https://cmake.org/cmake/help/latest/prop_tgt/CUDA_ARCHITECTURES.html] for more details. | "60;70" |
 
 ```Bash
 Usage: ./ac_run [options]
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 How do I compile with MPI support?
 
-> MPI implementation for Astaroth is still work in progress, these commands are for testing only. Invoke CMake with `cmake -DMPI_ENABLED=ON -DBUILD_SAMPLES=ON ..`. Otherwise the build steps are the same. Run with `mpirun -np 4 ./mpitest`.
+> Ensure that your MPI implementation has been built with CUDA support and invoke CMake with `cmake -DMPI_ENABLED=ON -DBUILD_SAMPLES=ON ..`. Otherwise the build steps are the same. Assign exactly one process per GPU and run with, for example, `srun --gres=gpu:v100:<ngpus per node> --ntasks-per-socket=<ngpus per node / NICs per node> -n <total number of gpus> -N <number of nodes> ./mpitest` or equivalent `mpirun` command.
 
 How do I contribute?