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Configuration and Dependencies
==============================

Configuration
-------------

.. tip::

    pressio-ops is header-only, so it does not need to be precompiled and linked to.

.. warning::

    To use pressio-ops, you need at least a C++17 compiler.

Dependencies
------------

Some parts contain code that are specific to third-party libraries (TPLs).
Currently, the list of TPLs supported is shown below:

.. list-table::
   :header-rows: 1
   :widths: 10 50 40
   :align: left

   * - TPL Name
     - Optional/Required
     - Version Known to Work/run in CI
   * - Eigen
     - Required
     - 3.4.0
   * - Trilinos
     - Optional
     - commits: 0dc4553, 5bbda25
   * - MPI
     - Optional
     - --
   * - Kokkos
     - Optional
     - 4.4.01
   * - BLAS
     - Optional
     - --
   * - LAPACK
     - Optional
     - --
   * - GoogleTest
     - Optional
     - 1.14.0

Eigen is the only required dependency because it is the
default choice for instantiating the ROM data structures
and solving the (dense) ROM problem used in `pressio <https://github.com/Pressio/pressio>`_.

Macros
~~~~~~

Enabling/disabling specific dependencies can be done via the following macros:

.. list-table::
   :widths: 30 60 10
   :header-rows: 1
   :align: left

   * - Variable
     - Description
     - Default

   * - ``PRESSIO_ENABLE_TPL_EIGEN``
     - self-explanatory
     - ``ON``

   * - ``PRESSIO_ENABLE_TPL_TRILINOS``
     - self-explanatory
     - ``OFF``

   * - ``PRESSIO_ENABLE_TPL_MPI``
     - self-explanatory
     - ``OFF`` but automatically ``ON`` if ``PRESSIO_ENABLE_TPL_TRILINOS=ON``

   * - ``PRESSIO_ENABLE_TPL_KOKKOS``
     - self-explanatory
     - ``OFF`` but automatically ``ON`` if ``PRESSIO_ENABLE_TPL_TRILINOS=ON``


Obviously, the choice of which TPLs to enable is related to
your application's dependency requirements.
For example, if you have an application that relies on
Trilinos data structures and want to use ``pressio-ops``\ ,
then it makes sense to enable the Trilinos dependency.
On the contrary, if you have an application that relies only on
Eigen data structures, then it makes sense to only leave only Eigen on
and disable the rest.

Also, we note that some of the macros listed above are connected.
For example, if we enable Trilinos then ``pressio-ops`` automatically
enables also Kokkos, BLAS, LAPACK and MPI.

Building
~~~~~~~~

``pressio-ops`` is a header-only library, and does not need to be built or installed.
However, one may use CMake to configure and build the tests by setting the ``-D PRESSIO_OPS_ENABLE_TESTS=ON`` CMake variable.

When configuring with CMake, all of the above macros may be passed as CMake variables.

.. important::

   Recall that to set a keyword in CMake you used the syntax ``-Dkeyword_name``.
   For example: ``-DPRESSIO_ENABLE_TPL_MPI=ON``