1.2.2 Choice of basic quantities

We choose the conserved variables

• density $\rho$,
• momentum $\rho\ensuremath{\mathchoice{\mbox{\boldmath$\displayst... ...ox{\boldmath$\scriptstyle v$}} {\mbox{\boldmath$\scriptscriptstyle v$}}}$,
• total energy $e_{\rm ik}$

as basic quantities, because they have

• no source terms (we ignore gravity here),
• simpler transport properties

rather than e.g. the primitive variables

• density $\rho$,
• velocity $\ensuremath{\mathchoice{\mbox{\boldmath$\displaystyle ... ...ox{\boldmath$\scriptstyle v$}} {\mbox{\boldmath$\scriptscriptstyle v$}}}$,
• pressure $P$.