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% Verbal description for system Density (Density_desc.tex)
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   The acausal bond graph of system \textbf{Density} is
   displayed in Figure \Ref{Density_abg} and its label
   file is listed in Section \Ref{sec:Density_lbl}.

This three port component computes the density $\rho$ of substance in
terms of the temperature $T$ and the pressure $P$. At the moment,
there are four forms dependent on the four forms of the component parameter:
\begin{enumerate}
\item \emph{density,incompressible,rho}
\item \emph{specific\_volume,incompressible,rho}
\item \emph{density,ideal\_gas,R}
\item \emph{specific\_volume,ideal\_gas,R}
\end{enumerate}

\begin{equation}
  y = 
  \begin{cases}
    \rho & \text{if the parameter is
      \emph{density,incompressible,rho}}\\
    \frac{1}{\rho} & \text{if the parameter is
      \emph{specific\_volume,incompressible,rho}}\\
    \frac{P}{RT} & \text{if the parameter is \emph{density,ideal\_gas,R}}\\
    \frac{RT}{P} & \text{if the parameter is
      \emph{specific\_volume,ideal\_gas,R}}
  \end{cases}
\end{equation}
where $\rho$ is the density of the incompressible fluid and $R$ the
universal gas constant of the ideal gas.
