[dune-pdelab] Dirichlet conditions on curved boundaries

[conf86 at web.de]

> reading this code I assume you want to define a function, which is 1
> on the boundary and 0 else.
> 
> This is not necessary. Just return 1. The reason is that you are
> computing an extension of the boundary values into the domain. The
> function is restricted to boundary DOFs afterwards.
> 
> Christian

Thank you for your answer.

Ok, first I thought to understand that. 
But now that I asked about initial conditions and found out that they are also defined in *bcextension this confuses me, because I now would expect if I return 1 wihtout any conditions that the initial values are set to 1 too. Or is this only the case if I use the interpolation like this and otherwise it is automatically 0?

> The vector ok unknowns is then usually set to values interpolated from the
> initial conditions by code like this:
> 
>   typedef BCExtension<GV,Real> G;                               // boundary value + extension
>   G g(gv);
>   Dune::PDELab::interpolate(g,gfs,u);                           // interpolate coefficient vector