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\section{Utilities}\label{sec:util}

\subsection{Introduction}

In this section, different utility modules and routines are assembled,
such as the {\tt time} module (see {\tt time.F90}), keeping track of all time
calculations, the {\tt mtridiagonal} module with a Gaussian solver for
systems of equations with tri-diagonal matrices (see {\tt
tridiagonal.F90}), and the {\tt eqstate} module (see {\tt
eqstate.F90}) with different versions of the equation of state.

Also discussed are advection and diffusion routines, such as {\tt
diff\_center()} and {\tt adv\_center()} for variables located
at the centers of the grid cells, i.e.\ in general mean flow
variables. 


