On Fri, Sep 6, 2013 at 1:33 PM, Jed Brown <[email protected]> wrote:
> Please send these questions to petsc-dev (Cc'd now) or petsc-users so > that others can comment. > > Lulu Liu <[email protected]> writes: > > > Hi, > > > > I want to implement ASPIN-like ideas, but based on field splitting. You > > could find the details in PDF file. > > You are proposing left-preconditioned nonlinear additive fieldsplit. > This is a sensible algorithm that we have discussed before. The only > part that needs to be implemented is the fieldsplit solve: separation of > G and H, then solving each separately. > > Unfortunately, I think it's kinda tricky to come up with a generally > useful interface. In particular, many applications cannot partition the > variables like you have done, meaning that the preconditioner is > becomes: change variables, solve in other bases, then change back. At > this point, I would recommend implementing the solve with \hat F using > SNESShell. > Did we throw away the SNES 'multiblock' code? It was supposed to do this. Matt > > My questions: > > > > I have a nonlinear system including two equations. In my implementation, > I > > need to solve each equation separately, also I need to solve the coupled > > system. I feel confused about ordering: > > > > I know the unknowns are ordered as [p1,s1,p2,s2,p3,s3,......] in PETSc, > > however, it seems that I need the variables like [p1,p2,p3,... > s1,s2,s3,...] > > No, just use a strided IS to describe each set of variables. You can > VecScatter from the packed/monolithic global vector to the split space. > > > Is there any example to do the similar things in PETSc? > > Do you have any ideas to implement the algorithm easier? > > How to quickly extract [p1,p2,...p_{N}] or [s1,s2,....] from > > [p1,p2,....s1,s2,s3,...] ? > > How to quickly get the composed [p1,p2,...s1,s2,....] if I have > [p1,p2,...] > > and [s1,s2,..]? > > > > -- What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener
