Two more questions, somewhat related maybe. Is there a practical case where one would use plain Jacobi preconditioning over ILU?
Also, what exactly is happening when one uses -pc_bjacobi_blocks 2 ? Thanks, Justin On Wed, Jan 13, 2016 at 9:37 PM, Justin Chang <[email protected]> wrote: > Thanks Satish, > > And yes I meant sequentially. > > On Wed, Jan 13, 2016 at 8:26 PM, Satish Balay <[email protected]> wrote: > >> On Wed, 13 Jan 2016, Justin Chang wrote: >> >> > Hi all, >> > >> > What exactly is the difference between these two preconditioners? When I >> > use them to solve a Galerkin finite element poisson problem, I get the >> > exact same performance (iterations, wall-clock time, etc). >> >> you mean - when you run sequentially? >> >> With block jacobi - you decide the number of blocks. The default is >> 1-block/proc >> i.e - for sequnetial run you have only 1block i.e the whole matrix. >> >> So the following are essentially the same: >> -pc_type bjacobi -pc_bjacobi_blocks 1 [default] -sub_pc_type ilu [default] >> -pc_type ilu >> >> Satish >> >> > Only thing is I can't seem to use ILU in parallel though. >> >> >
