This examples simulates a pulse in a 3D bar, the pulse is of the form::

.. math:: u_x = A \mathrm{sin}(\frac{2 \pi k}{L} X_x) e^{- \frac{\frac{2 \pi
k}{L} X_x}/{L}}^2

with :math:`u_x` and :math:`X_x` being the displacement and position in the
:math:`x` direction.