From: Karen Lee <kylkaren@gm...>  20100220 05:07:36

Thanks for your response! On Fri, Feb 19, 2010 at 6:01 PM, Roy Stogner <roystgnr@...>wrote: > > On Fri, 19 Feb 2010, Karen Lee wrote: > > const Real value = exact_solution(xf, yf); >> >> is the line that gives the value, so if I wanted to impose that the >> values at the boundary are 0, I just put 0 instead right? >> > > Right. In fact, in a linear system like ex3 the whole residual drops > out in this case, and homogeneous Dirichlet boundaries only end up > affecting your matrix. For nonlinear systems things are trickier > depending on your solver; see ex18 for an example. > > > My system is linear, so I'll just set things to 0. > The other thing is, I'm not sure whether BoundaryMesh can just locate >> the boundary. I use tetgen .node and .ele files, and it >> doesn't seem that the .face files are read by libmesh, and so I'm >> wondering how it's able to locate the boundary... Or do I add >> some tags and say that certain nodes and elements are on the boundary? >> > > The boundary is currently implicitly defined: if an element doesn't > have a neighbor on one side, that side is a boundary side. If a node > is on a boundary side, that node is a boundary node. > > That works fine for most domains, which are the interior of their own > closure. If you've got something more complicated, let us know, but > don't be too optimistic. We currently break when refining domains > with infinitely thin slits, for one embarrassing example. > My domain has no holes. Should be ok I guess =) Thanks, Karen 