4. Notes

^{1 There are equivalent definitions of $\mathcal{A}$ , for example, internal energy can be made strictly positive rather than pressure.}

² It's also preferable for these meshes to have good geometric properties, which improves the accuracy of the diagrams.

³ from now on, ${\mathit{U}}_K^n$ is therefore an approximation of the mean value of U in the K mesh at t = t ⁿ . For simplicity's...