examples/navier-stokes.md

+Navier-Stokes equation
+======================
+We consider the incompressible Navier-Stokes equation in a rectangular domain $`\Omega=(0,Lx)\times(0,Ly)`$,
+```math
+\partial_t\mathbf{u} - \nabla\cdot\big(\nu\mathbf{D}(\mathbf{u})\big) + (\mathbf{u}\cdot\nabla)\mathbf{u} + \nabla p = \mathbf{f},\qquad\text{ in }\Omega \\
+\nabla\cdot\mathbf{u} = 0
+```
+with velocity $`\mathbf{u}`$ and pressure $`p`$, w.r.t. to boundary conditions $`\mathbf{u}=\mathbf{g}`$ on $`\partial\Omega`$.