... in debug mode. (Optimized is much faster.) And note that this example is the nonlinear Bratu problem, which while very similar to a Laplacian, is not the same and performs multiple linear solves. On Oct 3, 2013 8:21 AM, "Matthew Knepley" <[email protected]> wrote:
> On Thu, Oct 3, 2013 at 8:04 AM, mary sweat <[email protected]> wrote: > >> Hi all >> I am very new to petsc and to c programming. I need to build a huge >> sparse matrix with a block structure. >> The problem is that my matrx may be huge (200000*200000) so i Need a way >> to define it through the kronecker product or memorizing just the >> overdiagonal, diagonal and subdiagonal block. >> Is it possible in petsc? any suggestions? >> thanks a million in advance >> > > This is the 2D Laplacian with a 5-point FD stencil. There are many PETSc > examples which > form and solve this. For example, here is an example: > > 1,640,961 unknowns (on the fine level) > > 8,199,681 nonzeros > > ./ex5 -da_grid_x 21 -da_grid_y 21 -da_refine 6 -ksp_rtol 1.0e-9 -pc_type > mg -pc_mg_levels 4 -snes_monitor -snes_view > > This takes 375s on my underpowered Mac Air laptop. > > Thanks, > > Matt > > -- > What most experimenters take for granted before they begin their > experiments is infinitely more interesting than any results to which their > experiments lead. > -- Norbert Wiener >
