[petsc-dev] stencils, ex2f.F, openmp

[Svetlana Tkachenko]

On Fri, 8 Nov 2013, at 15:17, Jed Brown wrote:
> Svetlana Tkachenko <svetlana.tkachenko at fastmail.fm> writes:
> > The example has a line to compute matrix A from Ax = b, and a line to compute source term (vector b).
> >
> >> call KSPSetComputeOperators(ksp,ComputeMatrix,ctx,ierr)
> >> call KSPSetComputeRHS(ksp,ComputeRHS,ctx,ierr)
> >
> > What do I use to give it the initial guess on x?
> 
> Those lines are registering callbacks, in order to have a uniform
> interface that can rediscretize the original operator and on coarse
> levels of multigrid.  Look at the implementation of ComputeMatrix and
> ComputeRHS for more.

Thank you.

I realised I have a set of dummy items to keep around the main matrix (1, x_dim, with only items 2 ... x_dim-1 included into matrix A itself). They are boundary conditions and the existing (serial) preconditioner relies on them.

In PETSC, I couldn't find examples with similar setup.