Stephan Kramer <[email protected]> writes: > An update on this. We have been using mark/gamg-zerod branch and it > fixes for us the issue with zero diagonals in the coarsened operators > (making the sor smoother, but bizarrely not the jacobi smoother fail). > We in fact have some cases where cheby+jacobi does not converge > (indefinite pc),
The most common cause of this is inaccurate eigenvalue bounds. You can try using more iterations for estimation. > but cheby+sor (with the mark/gamg-zerod branch) works well, so we'd be > very much interested in getting this (or something similar) merged in > master. Maybe the lv[i-Istart]==0.0 thing isn't entirely robust? We'd > be happy to contribute. > > As an aside, we also changed the ordering of DOFs as suggested, so that > we provide the right block structure to gamg. However, as soon as we > actually set the block size (MatSetBlockSizes) the convergence > deteriorates substantially (going from ~50 to ~650 iterations). Without > setting the block size but with the new ordering, the n/o iterations is > roughly the same as before (when our dofs were not interlaced). Any idea > what might be going wrong? Are you setting the block size and the rigid body modes (MatSetNearNullSpace, perhaps with MatNullSpaceCreateRigidBody)? Are those modes set using interlaced ordering?
pgp4f8J_TxzES.pgp
Description: PGP signature
