On Thu, Apr 6, 2017 at 7:39 AM, Kong, Fande <[email protected]> wrote: > Thanks, Mark and Barry, > > It works pretty wells in terms of the number of linear iterations (using > "-pc_gamg_sym_graph true"), but it is horrible in the compute time. I am > using the two-level method via "-pc_mg_levels 2". The reason why the compute > time is larger than other preconditioning options is that a matrix free > method is used in the fine level and in my particular problem the function > evaluation is expensive. > > I am using "-snes_mf_operator 1" to turn on the Jacobian-free Newton, but I > do not think I want to make the preconditioning part matrix-free. Do you > guys know how to turn off the matrix-free method for GAMG?
You do have an option to use the operator or the preconditioner operator (matrix) for the fine grid smoother, but I thought it uses the PC matrix by default. I don't recall the parameters nor do I see this in the view output. Others should be able to help.
