Hi, I am solving a variable coefficients Poisson equation with periodic BCs. The equation is discretized by using the standard 5-points stencil finite differencing scheme. I managed to solve the system successfullywith the PCG method and now I would like to add a preconditioner to speed up the calculation. My idea is to use the multigrid preconditioner.
Example ex22f.F implements what I think I need. If I understand correctly example ex22f.F, the subroutines "ComputeRHS" and "ComputeMatrix" define how the matrix and rhs-vector have to be computed at each level. In my case tough, both the jacobian and the rhs-vector cannot be computed "analytically", that is, they depend on variables whose values are available only at the finest grid. How can I overcome this difficulty? Thank you, Michele -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120730/607864a2/attachment.html>
