\item\code{getCelerity}:~The stability criterion of the explicit integration scheme depend on the fastest wave celerity~\eqref{eqn:smm:explicit:stabletime}. This celerity depend on the material, and therefore the value of this velocity should be defined in this method for each new material. By default, the fastest wave speed is the compressive wave whose celerity can be defined in~\code{getPushWaveSpeed}.
\end{itemize}
Once the declaration and implementation of the new material has been
completed, this material can be used in the user's example by including the header file:
\begin{cpp}
#include "material_XXX.hh"
\end{cpp}
For existing materials, as mentioned in Section~\ref{sect:smm:CL}, by
default, the materials are initialized inside the method
\code{initFull}. If a local material should be used instead, the
initialization of the material has to be postponed until the local
material is registered in the model. Therefore, the model is
initialized with the boolean for skipping the material initialization