.. _theory_multiblock:

**********
Multiblock
**********

The multiblock strategy for the LBM grid allows the existence of several refinement levels in the domain. 
The coarsest level is :math:`n=0` and the finest level is :math:`n=N`, where :math:`N` is the 
maximum level. 
The elementary volume consists of a cube of an integer size :math:`d`, called block. 
Every block in the domain, regardless of its refinement level, contains the same number of LBM nodes. 
When a block is refined, it subdivides in 8 cubes of size :math:`d/2`, see figure below:

.. figure:: /_static/img/theory/multiblock/refinement.svg
    :width: 70 %
    :align: center

Neighboring blocks of size :math:`d=4` are illustrated in the figure below:

.. figure:: /_static/img/theory/multiblock/mb-nodes.svg
    :width: 30 %
    :align: center

LBM nodes are shown in the frontal face. 
In the cell-vertex approach, each face of a block has :math:`(d)^2` nodes.


.. note::
    One important aspect of this approach is the recursiveness.
    So the same rules and properties applies when dividing a block from level 0 to 1 or 1 to 2, and so on.
    This allows the application of same communication rules, for example, for every level transition.

.. toctree::
   :maxdepth: 1
   :caption: Multiblock
   :hidden:

   Scaling<scaling.rst>
   Communication<communication.rst>