.. _InputsDomain:

Defining the domain
===================

All simulations, whether using an embedded boundary (EB) or not, are specified on a simple cuboid domain. The
low and high corners of the cuboid are defined by the ``prob_lo`` and ``prob_hi`` inputs.

The following inputs are defined using the prefix ``geometry``:

.. _InputsTable_domain:

+-----------------+-----------------------------------------------------------------------+-------------+-----------+
|                 | Description                                                           |   Type      | Default   |
+=================+=======================================================================+=============+===========+
| coord_sys       | Coordinate system used in simulation. Only Cartesian coordinates      |   Int       |   0       |
|                 | (``coord_sys = 0``) are supported.                                    |             |           |
+-----------------+-----------------------------------------------------------------------+-------------+-----------+
| is_periodic     | 1 for true, 0 for false (one value for each coordinate direction)     |   Ints<3>   | 0 0 0     |
+-----------------+-----------------------------------------------------------------------+-------------+-----------+
| prob_lo         | Low corner of physical domain (physical not index space)              |   Reals<3>  | 0 0 0     |
+-----------------+-----------------------------------------------------------------------+-------------+-----------+
| prob_hi         | High corner of physical domain (physical not index space)             |   Reals<3>  | 0 0 0     |
+-----------------+-----------------------------------------------------------------------+-------------+-----------+

.. attention::

   MFIX-Exa geometry restrictions:

   * There is **no support** for 1D or 2D simulation domains.
   * Cartesian is the **only supported** coordinate system.


Mesh
----

The following inputs are defined using the prefix ``amr``:

.. _InputsTable_mesh:

+----------------------+-----------------------------------------------------------------------+-------------+-----------+
|                      | Description                                                           |   Type      | Default   |
|                      |                                                                       |             |           |
+======================+=======================================================================+=============+===========+
| n_cell               | Number of cells at level 0 in each coordinate direction.              |    Ints<3>  | 0 0 0     |
+----------------------+-----------------------------------------------------------------------+-------------+-----------+

The base mesh spacing is computed for each direction by dividing the :ref:`domain length<InputsTable_domain>` by the
number of cells. The mesh spacing is required to be the same in all directions:

.. math::

   \frac{\text{prob_hi[0] - prob_lo[0]}}{\text{n_cell[0]}}
   = \frac{\text{prob_hi[1] - prob_lo[1]}}{\text{n_cell[1]}}
   = \frac{\text{prob_hi[2] - prob_lo[2]}}{\text{n_cell[2]}}


The inputs for defining the mesh for a single-level simulation are demonstrated in the
:ref:`following example<inputs_mesh_ex>` and  illustrated in :numref:`fig_basic_mesh_ex`.
In this example, the domain is a :math:`4 \times 1 \times 1` cuboid, and there are
:math:`32 \times 8 \times 8` cells in the *X*, *Y*, and *Z* directions, respectively.
The result is a uniform mesh spacing of :math:`0.125` *m* in all three directions.

.. _inputs_mesh_ex:

.. code-block:: bash
   :caption: Snippet of intpus for mesh example. This is not a complete input file.

   # Define periodicity and domain extents
   # -------------------------------------------------------------
   geometry.coord_sys   =  0           # Cartesian coordinates
   geometry.is_periodic =  0   0   0   # periodicity for each direction
   geometry.prob_lo     =  0.  0.  0   # lo corner of physical domain.
   geometry.prob_hi     =  4.  1.  1.  # hi corner of physical domain

   # Define the maximum level of refinement and number of cells
   # -------------------------------------------------------------
   amr.n_cell = 32  8  8


.. _fig_basic_mesh_ex:

.. figure:: ./images/geometry/mesh_lev0_ex.png
   :width: 100%
   :align: center
   :alt: domain used with box embedded boundary

   Example of a single-level mesh.

.. warning::

   MFIX-Exa simulations with a non-uniform mesh will not run.