On Mar 23, 2009, at 2:06 PM, Rafael Santos Coelho wrote: > Barry, > > sorry if I'm coming off stubborn or something, but I think I'm not > following your reasoning. > > NO. > > If you are using LU to construct a preconditioner then you ARE > providing the Jacobian explicitly (as a sparse) matrix. Each time > the preconditioner is built this sparse matrix is factored. > > What do you mean by "providing the jacobian explicity (as a sparse) > matrix"? I thought that there was no explicit jacobian matrix, but > only a MATMFFD context.
If so, then you are not using LU as a preconditioner; in fact you are not using a preconditioner at all. Run with -snes_view and send us the output to see what solver you are actually using. > > > Rafael
