Hello,
I have a few questions on how to improve performance of my program. I'm solving Poisson's equation on a (large) 3D FD grid with Dirichlet boundary conditions and multiple right hand sides. I set up the matrix and everything's working fine so far, but I'm sure the solving process could go faster. I know multigrid is generally the best preconditioner in such a case and algebraic multigrid currently works best. So generally speaking: Should I make the effort of symmetrizising the system matrix? I know how to do it, but it would probably take some time. CG does currently work, but is not competitive against other methods, so I guess the matrix might not be "symmetric enough"? For the various multigrid preconditioners: I always read that the problem should be solved exactly on the coarsest grid, but wouldn't an iterative solver do the same job if its provided accuracy is high enough, since the coarse discretization and the subsequent interpolation process introduce errors themselves? I submit my program to a batch system, but PETSc was compiled on the login node with different hardware. Is this affecting performance? What parts of the configuration process should I perform on a compute node then? Thanks.
