Barry, sorry but I can see that with a simpler version, mg starts to work with dof = 4. So maybe there are some bugs in my original code.
________________________________________ From: Sun, Hui Sent: Friday, February 27, 2015 6:25 PM To: Barry Smith Cc: petsc-users@mcs.anl.gov Subject: RE: [petsc-users] DMDA with dof=4, multigrid solver Sorry, I misread your email. I thought you were saying that it only handles dof = 1 fine. Sure I will send you the code. However, the code has some other dependencies. Let me remove those and send it to you in one file. Thanks a lot. ________________________________________ From: Barry Smith [bsm...@mcs.anl.gov] Sent: Friday, February 27, 2015 5:11 PM To: Sun, Hui Cc: petsc-users@mcs.anl.gov Subject: Re: [petsc-users] DMDA with dof=4, multigrid solver > On Feb 27, 2015, at 6:36 PM, Sun, Hui <hus...@ucsd.edu> wrote: > > I'm trying to work on 4 Poisson's equations defined on a DMDA grid, Hence the > parameter dof in DMDACreate3d should be 4, and I've set stencil width to be > 4, and stencil type to be star. Use a stencil width of 1, not 4. The stencil width is defined in terms of dof. > > If I run the code with -pc_type ilu and -ksp_type gmres, it works alright. > > However, if I run with pc_type mg, it gives me an error saying that when it > is doing MatSetValues, the argument is out of range, and there is a new > nonzero at (60,64) in the matrix. However, that new nonzero is expected to be > there, the row number 60 corresponds to i=15 and c=0 in x direction, and the > column number 64 corresponds to i=16 and c=0 in x direction. So they are next > to each other, and the star stencil with width 1 should include that. I have > also checked with the memory allocations, and I'm found no problem. > > So I'm wondering if there is any problem of using multigrid on a DMDA with > dof greater than 1? No it handles dof > 1 fine. Send your code. Barry > > Thank you!
