a C++ low Mach number stellar hydrodynamics code

MAESTROeX solves the equations of low Mach number hydrodynamics for stratified atmospheres/full spherical stars with a general equation of state, and nuclear reaction networks in an adaptive-grid finite-volume framework. It includes reactions and thermal diffusion and can be used on anything from a single core to 100,000s of processor cores with MPI + OpenMP or 1,000s of GPUs.

A description of the algorithm and links to the algorithm papers can be found here:

http://amrex-astro.github.io/MAESTROeX/

Getting started

• MAESTROeX requires a C++ compiler that supports the C++17 standard and a C compiler that supports the C99 standard. Several compiler suites are supported, including GNU, Intel, LLVM, and Cray. GNU Make (>= 3.82) is also required, as is Python (>= 3.9) and standard tools available in any Unix-like environments (e.g., Perl and sed).

  For GPU computing, CUDA 10 or later is required.

• To stay up-to-date with MAESTROeX, you will want to periodically pull changes from the repository by typing git pull.

• To get things running, you will need to get a copy of Microphysics and AMReX. Both are available on github separately or as submodules.

  To clone MAESTROeX with the submodules, do:

  git clone --recursive https://github.com/AMReX-Astro/MAESTROeX.git

  To add the submodules to an existing clone, from the top-level MAESTROeX directory, do:

  git submodule update --init --recursive

  If you want to get the AMReX and Microphysics separately, they can be directly cloned as:

  git clone https://github.com/AMReX-Astro/Microphysics.git
  git clone https://github.com/AMReX-Codes/amrex.git

• You will then need to setup your shell environment to tell MAESTROeX where to find AMReX and Microphysics. Define the AMREX_HOME environment variable to point to the amrex/ directory, and MICROPHYSICS_HOME environment variable to point to the Microphysics/ directory. For example, if your shell is Bash:

  export AMREX_HOME="/path/to/amrex/"
  export MICROPHYSICS_HOME='/path/to/Microphysics"

  Note: you must specify the full path to the directories. Do not use ∼ to refer to your home directory; the scripts used by the build system will not be able to process this.

• Change directory to correspond to the problem that you want to run. Each problem lives under one of three sub-directories of MAESTROeX/Exec/: SCIENCE/, TEST_PROBLEMS/, or UNIT_TESTS/. Then build the executable and run it by specifying an input file.

  • For example, to run the standard reacting_bubble problem in 2-D:

    cd MAESTROeX/Exec/TEST_PROBLEMS/reacting_bubble/
    make DIM=2
    ./Maestro2d.gnu.ex inputs_2d_C

• The plotfiles (named pltXXXXXXX) are in BoxLib/AMReX format and can be visualized using yt, Amrvis, and VisIt.

For more detailed instructions on how to run the code and available test problems, refer to MAESTROeX User's Guide:

https://amrex-astro.github.io/MAESTROeX/docs/getting_started.html

Regression and unit testing

MAESTROeX needs to be tested in tandem with the AMReX and Microphysics repo updates. We use github CI as well as testing on local machines using the AMReX regression test framework (https://github.com/AMReX-Codes/regression_testing). Tests are run nightly and reported here:

https://ccse.lbl.gov/pub/RegressionTesting/MAESTROeX/ http://groot.astro.sunysb.edu/MAESTROeX/test-suite/gfortran/

A number of small unit tests exist in Exec/UNIT_TESTS for testing physics solvers independently.

Development Model:

Development generally follows the following ideas:

• New features are committed to the development branch.

  Nightly regression testing is used to ensure that no answers change (or if they do, that the changes were expected).

  If a change is critical, we can cherry-pick the commit from development to main.

• Contributions are welcomed from anyone. Any contributions that have the potential to change answers should be done via pull requests. A pull request should be generated from your fork of MAESTROeX and target the development branch. (If you mistakenly target main, we can change it for you.)

  If there are a number of small commits making up the PR, we may wish to squash commits upon merge to have a clean history. Please ensure that your PR title and first post are descriptive, since these will be used for a squashed commit message.

• On the first workday of each month, we perform a merge of development into main, in coordination with AMReX, MAESTROeX, and Microphysics. For this merge to take place, we need to be passing the regression tests.

  To accommodate this need, we close the merge window into development a few days before the merge day. While the merge window is closed, only bug fixes should be pushed into development. Once the merge from development -> main is done, the merge window reopens.

Core Developers

People who make a number of substantive contributions will be named "core developers" of MAESTROeX. The criteria for becoming a core developer are flexible, but generally involve one of the following:

• 10 non-merge commits to MAESTROeX/Source/ or MAESTROeX/sphinx_docs/ or one of the problems that is not your own science problem or

• addition of a new algorithm / module or

• substantial input into the code design process or testing

Core developers will be recognized in the following ways:

• invited to the group's slack team

• listed in the User's Guide and website as a core developer

• listed in the author list on the Zenodo DOI for the project (as given in the .zenodo.json file)

• invited to co-author general code papers / proceedings describing MAESTROeX, its performance, etc. (Note: science papers will always be left to the science leads to determine authorship).

If a core developer is inactive for 3 years, we may reassess their status as a core developer.

Getting help

For answers to frequently asked questions and solutions to common problems, consult the FAQ section of the User's Guide.

If you discover any bugs in the code or would like to request further help, then please submit a issue to the MAESTROeX Github repository describing your problem.

For general questions, post to the discussion forum: https://github.com/AMReX-Astro/MAESTROeX/discussions

and for problems, raise an issue: https://github.com/AMReX-Astro/MAESTROeX/issues