Poisson equation
================

The laplacian in a square is the usual starting point of PDEs.

.. note::
    The problem is optionnally solved as non-linear in a Newton algorithm in order to be convinced of the correctness of the formulation.

.. note::
    An *analytical solution* may be given as an expression to be compared with. Note that it is the same expression than the imposed
    value at the boundaries. It is better have them equal on that common zone ...


.. literalinclude:: ./nvi_Poisson_0.cpp
    :language: c++

Results
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.. figure:: Poisson30x30.png
    :align: center