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CONTRIBUTING.md

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Contribute to WarpX

We welcome new contributors! Here is how to participate to the WarpX development.

Git workflow

The WarpX project uses git for version control. If you are new to git, you can follow one of these tutorials:

Make your own fork and create a branch on it

The basic WarpX workflow is:

  • fork the main repo (or update it if you already created it);
  • Implement your changes and push them on a new branch <branch_name> on your fork;
  • Create a Pull Request from branch <branch_name> on your fork to branch dev on the main WarpX repo.

First, let us setup your local git repo. Make your own fork of the main (upstream) WarpX repo: on the WarpX Github page, press the fork button. Then, you can execute:

# These 4 first lines are the same as for a standard WarpX install
mkdir warpx_directory
cd warpx_directory
git clone --branch master https://bitbucket.org/berkeleylab/picsar.git
git clone --branch development https://github.com/AMReX-Codes/amrex.git

# Clone your fork on your local computer. You can get this address on your fork's Github page.
git clone --branch dev https://github.com/<myGithubUsername>/ECP-WarpX/WarpX.git
cd warpx
# Keep track of the main WarpX repo, to remain up-to-date.
git remote add upstream https://github.com/ECP-WarpX/WarpX.git

Now you are free to play with your fork (for additional information, you can visit the Github fork help page).

Note: you do not have to re-do the setup above every time. Instead, in the future, you need to update the dev branch on your fork with

git checkout dev
git pull upstream dev

Make sure you are on WarpX dev branch with

git checkout dev

in the WarpX directory.

Create a branch <branch_name> (the branch name should reflect the piece of code you want to add, like fix_spectral_solver) with

git checkout -b <branch_name>

and do the coding you want. It is probably a good time to look at the AMReX documentation and at the AMReX Doxygen reference. Add the files you work on to the git staging area with

git add <file_I_created> <and_file_I_modified>

Commit & push your changes

Periodically commit your changes with

git commit -m "This is a 50-char description to explain my work"

The commit message (between quotation marks) is super important in order to follow the developments and identify bugs.

For the moment, commits are on your local repo only. You can push them to your fork with

git push -u origin <branch_name>

If you want to synchronize your branch with the dev branch (this is useful when the dev branch is being modified while you are working on <branch_name>), you can use

git pull upstream dev

and fix any conflict that may occur.

Check that you did not break the code

Once your new feature is ready, you can check that you did not break anything. WarpX has automated tests running for each Pull Request. For easier debugging, it can be convenient to run the tests on your local machine with

./run_tests.sh

from WarpX root folder. The tests can be influenced by environment variables:

  • export WARPX_TEST_DIM=3 or export WARPX_TEST_DIM=2 in order to select only the tests that correspond to this dimension
  • export WARPX_TEST_ARCH=CPU or export WARPX_TEST_ARCH=GPU in order to run the tests on CPU or GPU respectively.
  • export WARPX_TEST_COMMIT=... in order to test a specific commit.

Submit a Pull Request

A Pull Request (PR) is the way to efficiently visualize the changes you made and to propose your new feature/improvement/fix to the WarpX project. Right after you push changes, a banner should appear on the Github page of your fork, with your <branch_name>.

  • Click on the compare & pull request button to prepare your PR.
  • Change the PR destination from master to dev (make sure that the PR is from <yourFork>/<branch_name> to ECP-WarpX/WarpX/dev).
  • It is time to communicate your changes: write a title and a description for your PR. People who review your PR are happy to know
    • what feature/fix you propose, and why
    • how you made it (created a new class than inherits from...)
    • and anything relevant to your PR (performance tests, images, etc.)
  • Press Create pull request. Now you can navigate through your PR, which highlights the changes you made.

Pull Requests DO NOT have to be large: it is much easier to review small targeted PRs than a huge chunk of code, so feel free to split your work in small pieces.

Even before your work is ready to merge, it can be convenient to create a PR (so you can use Github tools to visualize your changes). In this case, please put the [WIP] tag (for Work In Progress) at the beginning of the PR title.

Include a test to your PR

A new feature is great, a working new feature is even better! Please test your code and add your test to the automated test suite. It's the way to protect your work from adventurous developers. There are three steps to follow to add a new automated test (illustrated here for PML boundary conditions):

  • An input file for your test, in folder Example/Tests/.... For the PML test, the input file is at Examples/Tests/PML/inputs2d. You can also re-use an existing input file (even better!) and pass specific parameters at runtime (see below).
  • A Python script that reads simulation output and tests correctness versus theory or calibrated results. For the PML test, see Examples/Tests/PML/analysis_pml.py. It typically ends with Python statement assert( error<0.01 ).
  • Add an entry to Regression/WarpX-tests.ini, so that a WarpX simulation runs your test in the continuous integration process on Travis CI, and the Python script is executed to assess the correctness. For the PML test, the entry is
[pml_x_yee]
buildDir = .
inputFile = Examples/Tests/PML/inputs2d
runtime_params = warpx.do_dynamic_scheduling=0 algo.maxwell_fdtd_solver=yee
dim = 2
addToCompileString =
restartTest = 0
useMPI = 1
numprocs = 2
useOMP = 1
numthreads = 2
compileTest = 0
doVis = 0
analysisRoutine = Examples/Tests/PML/analysis_pml_yee.py

If you re-use an existing input file, you can add arguments to runtime_params, like runtime_params = amr.max_level=1 amr.n_cell=32 512 max_step=100 plasma_e.zmin=-200.e-6 .

Include documentation to your PR

Now, let users know about your new feature by adding it to the WarpX documentation. Our documentation uses Sphinx, and it is located in Docs/. For instance, if you introduce a new runtime parameter in the input file, you can add it to Docs/source/running_cpp/parameters.rst. If Sphinx is installed on your computer, you should be able to generate the html documentation with

make html

in Docs/. Then open html/index.html with your favorite web browser and look for your changes.

Once your code is ready with documentation and automated test, congratulations! you can create the PR (or remove the [WIP] tag if you already created it). Reviewers will interact with you if they have comments/questions.

Style and conventions

  • For indentation, WarpX uses four spaces (no tabs)
  • The number of characters per line should be <80
  • To define a function , for e.g., myfunction() use a space between the name of the function and the paranthesis - myfunction (). To call the function, the space is not required, i.e., just use myfunction(). The reason this is beneficial is that when we do a 'git grep ' to search for myfunction (), we can clearly see the locations where myfunction () is defined and where myfunction() is called.
  • Also, using 'git grep "myfunction ()"' searches for files only in the git repo, which is more efficient compared to the 'grep "myfunction ()"' command that searches through all the files in a directory, including plotfiles for example.
  • It is recommended that style changes are not included in the PR where new code is added. This is to avoid any errors that may be introduced in a PR just to do style change.
  • Some text editors automatically modify the files you open (e.g., to remove trailing spaces). Please turn this feature off as it causes many changes and makes pull requests harder to review.
  • #include directives should be ordered from more specific to more general, i.e., "module header", "WarpX header", <close library headers> (AMReX, PICSAR), <other third party headers> (e.g., omp), <stdlib headers>. See PR #331, or LLVM or include-what-you-use pages.
  • WarpX uses CamelCase convention for file names and class names, rather than snake_case.