Building from source
====================

First, obtain the JAX source code.

.. code-block:: shell

    git clone https://github.com/google/jax
    cd jax


There are two steps to building JAX: building ``jaxlib`` and installing ``jax``.

If you're only modifying Python portions of JAX, you may be able to install
``jaxlib`` from pip or a prebuilt wheel and skip to installing ``jax`` from
source.

To build ``jaxlib``, you must also install some prerequisites:
 * a C++ compiler (g++ or clang)
 * Numpy
 * Scipy
 * Cython

On Ubuntu 18.04 or Debian you can install the necessary prerequisites with:

.. code-block:: shell

 sudo apt-get install g++ python python3-dev python3-numpy python3-scipy cython3


If you are building on a Mac, make sure XCode and the XCode command line tools
are installed.

You can also install the necessary Python dependencies using ``pip``:

.. code-block:: shell

 pip install numpy scipy cython


To build ``jaxlib`` with CUDA support, you can run

.. code-block:: shell

    python build/build.py --enable_cuda
    pip install -e build  # installs jaxlib (includes XLA)


See ``python build/build.py --help`` for configuration options, including ways to
specify the paths to CUDA and CUDNN, which you must have installed. The build
also depends on NumPy, and a compiler toolchain corresponding to that of
Ubuntu 16.04 or newer.

To build ``jaxlib`` without CUDA GPU support (CPU only), drop the ``--enable_cuda``:

.. code-block:: shell

  python build/build.py
  pip install -e build  # installs jaxlib (includes XLA)

Once ``jaxlib`` has been installed, you can install ``jax`` by running

.. code-block:: shell

  pip install -e .  # installs jax

To upgrade to the latest version from GitHub, just run ``git pull`` from the JAX
repository root, and rebuild by running ``build.py`` or upgrading ``jaxlib`` if
necessary. You shouldn't have to reinstall because ``pip install -e`` sets up
symbolic links from site-packages into the repository.

Running the tests
=================

To run all the JAX tests, we recommend using ``pytest-xdist``, which can run tests in
parallel. First, install ``pytest-xdist`` by running ``pip install pytest-xdist``.
Then, from the repository root directory run

.. code-block:: shell

 pytest -n auto tests


JAX generates test cases combinatorially, and you can control the number of
cases that are generated and checked for each test (default is 10). The automated tests
currently use 25:

.. code-block:: shell

 JAX_NUM_GENERATED_CASES=25 pytest -n auto tests

The automated tests also run the tests with default 64-bit floats and ints:

.. code-block:: shell

 JAX_ENABLE_X64=1 JAX_NUM_GENERATED_CASES=25 pytest -n auto tests

You can run a more specific set of tests using
`pytest <https://docs.pytest.org/en/latest/usage.html#specifying-tests-selecting-tests>`_'s
built-in selection mechanisms, or alternatively you can run a specific test
file directly to see more detailed information about the cases being run:

.. code-block:: shell

 python tests/lax_numpy_test.py --num_generated_cases=5

The Colab notebooks are tested for errors as part of the documentation build.

Update documentation
====================

To rebuild the documentation, install several packages:

.. code-block:: shell

  pip install -r docs/requirements.txt

You must also install ``pandoc`` in order to regenerate the notebooks.
See `Install Pandoc <https://pandoc.org/installing.html>`_. On Mac, I had success with
the miniconda installer, then ``conda install -c conda-forge pandoc``.
If you do not want to install ``pandoc`` then you should regenerate the documentation
without the notebooks.

You run at top-level one of the following commands:

.. code-block:: shell

  sphinx-build -b html docs docs/build/html  # with the notebooks
  sphinx-build -b html -D nbsphinx_execute=never docs docs/build/html  # without the notebooks

You can then see the generated documentation in
``docs/build/html/index.html``.

Update notebooks
----------------

Open the notebook with http://colab.research.google.com, update it, ``Run all cells`` then
``Download ipynb``. You may want to test that it executes properly, using ``sphinx-build`` as
explained above.

Documentation building on readthedocs.io
----------------------------------------

JAX's auto-generated documentations is at `jax.readthedocs.io <https://jax.readthedocs.io/>`_.

The documentation building is controlled for the entire project by the
`readthedocs JAX settings <https://readthedocs.org/dashboard/jax>`_. The current settings
trigger a documentation build as soon as code is pushed to the GitHub ``master`` branch.
For each code version, the building process is driven by the
``.readthedocs.yml`` and the ``docs/conf.py`` configuration files.

For each automated documentation build you can see the
`documentation build logs <https://readthedocs.org/projects/jax/builds/>`_.

If you want to test the documentation generation on Readthedocs, you can push code to the ``test-docs``
branch. That branch is also built automatically, and you can
see the generated documentation `here <https://jax.readthedocs.io/en/test-docs/>`_.

For a local test, I was able to do it in a fresh directory by replaying the commands
I saw in the Readthedocs logs:

.. code-block:: shell

    mkvirtualenv jax-docs  # A new virtualenv
    mkdir jax-docs  # A new directory
    cd jax-docs
    git clone --no-single-branch --depth 50 https://github.com/google/jax
    cd jax
    git checkout --force origin/test-docs
    git clean -d -f -f
    
    python -m pip install --upgrade --no-cache-dir pip
    python -m pip install --upgrade --no-cache-dir -I Pygments==2.3.1 setuptools==41.0.1 docutils==0.14 mock==1.0.1 pillow==5.4.1 alabaster>=0.7,<0.8,!=0.7.5 commonmark==0.8.1 recommonmark==0.5.0 'sphinx<2' 'sphinx-rtd-theme<0.5' 'readthedocs-sphinx-ext<1.1'
    python -m pip install --exists-action=w --no-cache-dir -r docs/requirements.txt
    
    python `which sphinx-build` -T -E -b html -d _build/doctrees-readthedocs -D language=en . _build/html