# Tag Info

You cannot specify just a boundary condition on $\partial_x u$ at $x_L$. Remember that in DG your solution is composed of piecewise discontinuous polynomials; at every interface you can have effectively any jump in $u$, which is separate from the slope of u to the left or right of the interface. Unless $f(u,x)$ has any dependence on $\partial_x u$ (in which ...