On Tue, Aug 19, 2008 at 07:27:58AM -0500, Matthew Knepley wrote: > On Tue, Aug 19, 2008 at 7:06 AM, Anders Logg <[EMAIL PROTECTED]> wrote: > > On Tue, Aug 19, 2008 at 01:49:22PM +0200, Jed Brown wrote: > >> On Tue 2008-08-19 13:40, Anders Logg wrote: > >> > On Tue, Aug 19, 2008 at 12:12:50PM +0200, Jed Brown wrote: > >> > > On Tue 2008-08-19 11:59, Anders Logg wrote: > >> > > > On Thu, Aug 14, 2008 at 10:10:03PM +0000, Jed Brown wrote: > >> > > > > One way to implement this is to allocate a vector for Dirichlet > >> > > > > values, > >> > > > > a vector for Homogeneous values, and a Combined vector. The > >> > > > > Homogeneous > >> > > > > vector is the only one that is externally visible. > >> > > > > >> > > > Isn't this problematic? I want the entire vector visible externally > >> > > > (and not the homogeneous part). It would make it difficult to plot > >> > > > solutions, saving to file etc. > >> > > > > >> > > > Maybe the Function class could handle the wrapping but it would > >> > > > involve a > >> > > > complication. > >> > > > >> > > Right, by `externally visible' I mean to the solution process, that is > >> > > time-stepping, nonlinear solver, linear solvers, preconditioners. The > >> > > vector you are concerned about is the post-processed state which you > >> > > can > >> > > get with zero communication. It is inherently tied to the mesh and > >> > > anything you do with it likely needs to know mesh connectivity. I > >> > > don't > >> > > think it is advantageous to lump this in with the global state vector. > >> > > > >> > > Jed > >> > > >> > I don't understand. What is the global state vector? > >> > >> The global state vector is the vector that the solution process sees. > >> Every entry in this vector is a real degree of freedom (Dirichlet > >> conditions have been removed). This is the vector used for computing > >> norms, applying matrices, etc. When writing a state to a file, this > >> global vector is scattered to a local vector and boundary conditions are > >> also scattered into the local vector. The local vector is serialized > >> according to ownership of the mesh (you have to do this anyway). > >> > >> Jed > > > > I'm only worried about how to create a simple interface. Now, one may > > do > > > > u = Function(...); > > A = assemble(a, mesh) > > b = assemble(L, mesh) > > bc.apply(A, b) > > solve(A, u.x(), b) > > plot(u) > > > > How would this look if we were to separate out Dirichlet dofs? > > This is why we have a restrict/update() paradigm, whereas we have > different assemblies > for global vectors. The assemble would produce a system without BCs. > However, plot() > must access values in 'u', with restrict() which would give back all > values including BCs. > This is how it currently works in PETSc, so we can have this paradigm. > > Matt
I don't mind restrict()/update() but to me those are low-level operations that shouldn't be visible in the user-interface. -- Anders
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