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Inverse Problem PYthon library
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How to Contribute

The hIPPYlib team welcomes contributions at all levels: bugfixes, code improvements, new capabilities, improved documentation, or new examples/tutorials.

Use a pull request (PR) toward the hippylib:master branch to propose your contribution. If you are planning significant code changes, or have any questions, you should also open an issue before issuing a PR.

See the Quick Summary section for the main highlights of our GitHub workflow. For more details, consult the following sections and refer back to them before issuing pull requests:

Contributing to hIPPYlib requires knowledge of Git and, likely, inverse problems. If you are new to Git, see the GitHub learning resources. To learn more about inverse problems, see our tutorial page.

By submitting a pull request, you are affirming the Developer’s Certificate of Origin at the end of this file.

Quick Summary

  • We encourage you to join the hIPPYlib organization and create development branches off hippylib:master.
  • Please follow the developer guidelines, in particular with regards to documentation and code styling.
  • Pull requests should be issued toward hippylib:master. Make sure to check the items off the Pull Request Checklist.
  • After approval, hIPPYlib developers merge the PR in hippylib:master.
  • Don’t hesitate to contact us if you have any questions.

GitHub Workflow

The GitHub organization,, is the main developer hub for the hIPPYlib project.

If you plan to make contributions or will like to stay up-to-date with changes in the code, *we strongly encourage you to join the hIPPYlib organization*.

This will simplify the workflow (by providing you additional permissions), and will allow us to reach you directly with project announcements.

hIPPYlib Organization

New Feature Development

  • A new feature should be important enough that at least one person, the proposer, is willing to work on it and be its champion.

  • The proposer creates a branch for the new feature (with suffix -dev), off the master branch, or another existing feature branch, for example:

    # Clone assuming you have setup your ssh keys on GitHub:
    git clone
    # Alternatively, clone using the "https" protocol:
    git clone
    # Create a new feature branch starting from "master":
    git checkout master
    git pull
    git checkout -b feature-dev
    # Work on "feature-dev", add local commits
    # ...
    # (One time only) push the branch to github and setup your local
    # branch to track the github branch (for "git pull"):
    git push -u origin feature-dev
  • We prefer that you create the new feature branch as a fork. To allow hIPPYlib developers to edit the PR, please enable upstream edits.

  • The typical feature branch name is new-feature-dev, e.g. optimal_exp_design-dev. While not frequent in hIPPYlib, other suffixes are possible, e.g. -fix, -doc, etc.

Developer Guidelines

  • Keep the code lean and as simple as possible
    • Well-designed simple code is frequently more general and powerful.
    • Lean code base is easier to understand by new collaborators.
    • New features should be added only if they are necessary or generally useful.
    • Code must be compatible with Python 3.
    • When adding new features add an example in the application folder and/or a new notebook in the tutorial folder.
    • The preferred way to export solutions for visualization in paraview is using dl.XDMFFile
  • Keep the code general and reasonably efficient
    • Main goal is fast prototyping for research.
    • When in doubt, generality wins over efficiency.
    • Respect the needs of different users (current and/or future).
  • Keep things separate and logically organized
    • General usage features go in hIPPYlib (implemented in as much generality as possible), non-general features go into external apps/projects.
    • Inside hIPPYlib, compartmentalize between modeling, algorithms, utils, etc.
    • Contributions that are project-specific or have external dependencies are allowed (if they are of broader interest), but should be #ifdef-ed and not change the code by default.
  • Code specifics
    • All significant new classes, methods and functions have sphinx-style documentation in source comments.
    • Code styling should resemble existing code.
    • When manually resolving conflicts during a merge, make sure to mention the conflicted files in the commit message.

Pull Requests

  • When your branch is ready for other developers to review / comment on the code, create a pull request towards hippylib:master.

  • Pull request typically have titles like:

    Description [new-feature-dev]

    for example:

    Bayesian Optimal Design of Experiments [oed-dev]

    Note the branch name suffix (in square brackets).

  • Titles may contain a prefix in square brackets to emphasize the type of PR. Common choices are: [DON'T MERGE], [WIP] and [DISCUSS], for example:

    [DISCUSS] Bayesian Optimal Design of Experiments [oed-dev]

  • Add a description, appropriate labels and assign yourself to the PR. The hIPPYlib team will add reviewers as appropriate.

  • List outstanding TODO items in the description.

  • Track the Travis CI continuous integration builds at the end of the PR. These should run clean, so address any errors as soon as possible.

Pull Request Checklist

Before a PR can be merged, it should satisfy the following:

  • [ ] CI runs without errors.
  • [ ] Update CHANGELOG:
    • [ ] Is this a new feature users need to be aware of? New or updated application or tutorial?
    • [ ] Does it make sense to create a new section in the CHANGELOG to group with other related features?
  • [ ] New examples/applications/tutorials:
    • [ ] All new examples/applications/tutorials run as expected.
    • [ ] Add a fast version of the example/application/tutorial to Travis CI
  • [ ] New capability:
    • [ ] All significant new classes, methods and functions have sphinx-style documentation in source comments.
    • [ ] Add new examples/applications/tutorials to highlight the new capability.
    • [ ] For new classes, functions, or modules, edit the corresponding .rst file in the doc folder.
    • [ ] If this is a major new feature, consider mentioning in the short summary inside README (rare).
    • [ ] If this is a C++ extension, the package_data dictionary in should include new files.

Automated Testing

We use Travis CI to drive the default tests on the master and feature branches. See the .travis file and the logs at

Testing using Travis CI should be kept lightweight, as there is a 50 minute time constraint on jobs.

  • Tests on the master branch are triggered whenever a push is issued on this branch.

Contact Information

  • Contact the hIPPYlib team by posting to the GitHub issue tracker. Please perform a search to make sure your question has not been answered already.

Slack channel

The hIPPYlib slack channel is a good resource to request and receive help with using hIPPYlib. Everyone is invited to read and take part in discussions. Discussions about development of new features in hIPPYlib also take place here. You can join our Slack community by filling in this form.

Developer’s Certificate of Origin 1.1

By making a contribution to this project, I certify that:

  1. The contribution was created in whole or in part by me and I have the right to submit it under the open source license indicated in the file; or
  2. The contribution is based upon previous work that, to the best of my knowledge, is covered under an appropriate open source license and I have the right under that license to submit that work with modifications, whether created in whole or in part by me, under the same open source license (unless I am permitted to submit under a different license), as indicated in the file; or
  3. The contribution was provided directly to me by some other person who certified (a), (b) or (c) and I have not modified it.
  4. I understand and agree that this project and the contribution are public and that a record of the contribution (including all personal information I submit with it, including my sign-off) is maintained indefinitely and may be redistributed consistent with this project or the open source license(s) involved.

Acknowledgement: We thank the MFEM team for allowing us to use their contributing guidelines file as template.