On Fri, Jul 26, 2013 at 4:22 PM, Matthew Knepley <[email protected]> wrote:
> On Fri, Jul 26, 2013 at 9:11 AM, Bishesh Khanal <[email protected]>wrote: > >> >> >> >> On Fri, Jul 26, 2013 at 2:32 PM, Matthew Knepley <[email protected]>wrote: >> >>> On Fri, Jul 26, 2013 at 7:28 AM, Bishesh Khanal <[email protected]>wrote: >>> >>>> >>>> >>>> >>>> On Wed, Jul 17, 2013 at 9:48 PM, Jed Brown <[email protected]>wrote: >>>> >>>>> Bishesh Khanal <[email protected]> writes: >>>>> >>>>> > Now, I implemented two different approaches, each for both 2D and >>>>> 3D, in >>>>> > MATLAB. It works for the smaller sizes but I have problems solving >>>>> it for >>>>> > the problem size I need (250^3 grid size). >>>>> > I use staggered grid with p on cell centers, and components of v on >>>>> cell >>>>> > faces. Similar split up of K to cell center and faces to account for >>>>> the >>>>> > variable viscosity case) >>>>> >>>>> Okay, you're using a staggered-grid finite difference discretization of >>>>> variable-viscosity Stokes. This is a common problem and I recommend >>>>> starting with PCFieldSplit with Schur complement reduction (make that >>>>> work first, then switch to block preconditioner). >>>> >>>> >>>> Ok, I made my 3D problem work with PCFieldSplit with Schur complement >>>> reduction using the options: >>>> -pc_fieldsplit_type schur -pc_fieldsplit_detect_saddle_point >>>> -fieldsplit_1_ksp_constant_null_space >>>> >>>> >>>> You can use PCLSC or >>>>> (probably better for you), assemble a preconditioning matrix containing >>>>> the inverse viscosity in the pressure-pressure block. This diagonal >>>>> matrix is a spectrally equivalent (or nearly so, depending on >>>>> discretization) approximation of the Schur complement. The velocity >>>>> block can be solved with algebraic multigrid. Read the PCFieldSplit >>>>> docs (follow papers as appropriate) and let us know if you get stuck. >>>>> >>>> >>>> Now, I got a little confused in how exactly to use command line >>>> options to use multigrid for the velocity bock and PCLS for the pressure >>>> block. After going through the manual I tried the following: >>>> >>> >>> You want Algebraic Multigrid >>> >>> -pc_type fieldsplit -pc_fieldsplit_detect_saddle_point >>> -pc_fieldsplit_type schur >>> -fieldsplit_0_pc_type gamg >>> -fieldsplit_1_ksp_type fgmres >>> -fieldsplit_1_ksp_constant_null_space >>> -fieldsplit_1_ksp_monitor_short >>> -fieldsplit_1_pc_type lsc >>> -ksp_converged_reason >>> >>> I tried the above set of options but the solution I get seem to be not >> correct. The velocity field I get are quite different than the one I got >> before without using gamg which were the expected one. >> Note: (Also, I had to add one extra option of >> -fieldsplit_1_ksp_gmres_restart 100 , because the fieldsplit_1_ksp residual >> norm did not converge within default 30 iterations before restarting). >> > > These are all iterative solvers. You have to make sure everything > converges. > When I set restart to 100, and do -ksp_monitor, it does converge (for the fieldsplit_1_ksp). Are you saying that in spite of having -ksp_converged_reason in the option and petsc completing the run with the message "Linear solve converged due to CONVERGED_RTOL .." not enough to make sure that everything is converging ? If that is the case what should I do for this particular problem ? I have used the MAC scheme with indexing as shown in: fig 7.5, page 96 of: http://books.google.co.uk/books?id=W83gxp165SkC&printsec=frontcover&dq=Introduction+to+Numerical+Geodynamic+Modelling&hl=en&sa=X&ei=v6TmUaP_L4PuOs3agJgE&ved=0CDIQ6AEwAA Thus I have a DM with 4 dof but there are several "ghost values" set to 0. Would this cause any problem when using the multigrid ? (This has worked fine when not using the multigrid.) > I do this problem in the tutorial with > a constant viscosity. > Which tutorial are you referring to ? Could you please provide me the link please ? > Matt > > >> Matt >>> >>> >>>> but I get the following errror: >>>> >>>> [0]PETSC ERROR: --------------------- Error Message >>>> ------------------------------------ >>>> [0]PETSC ERROR: Null argument, when expecting valid pointer! >>>> [0]PETSC ERROR: Null Object: Parameter # 2! >>>> [0]PETSC ERROR: >>>> ------------------------------------------------------------------------ >>>> [0]PETSC ERROR: Petsc Release Version 3.4.2, Jul, 02, 2013 >>>> [0]PETSC ERROR: See docs/changes/index.html for recent updates. >>>> [0]PETSC ERROR: See docs/faq.html for hints about trouble shooting. >>>> [0]PETSC ERROR: See docs/index.html for manual pages. >>>> [0]PETSC ERROR: >>>> ------------------------------------------------------------------------ >>>> [0]PETSC ERROR: src/AdLemMain on a arch-linux2-cxx-debug named edwards >>>> by bkhanal Fri Jul 26 14:23:40 2013 >>>> [0]PETSC ERROR: Libraries linked from >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/arch-linux2-cxx-debug/lib >>>> [0]PETSC ERROR: Configure run at Fri Jul 19 14:25:01 2013 >>>> [0]PETSC ERROR: Configure options --with-cc=gcc --with-fc=g77 >>>> --with-cxx=g++ --download-f-blas-lapack=1 --download-mpich=1 >>>> -with-clanguage=cxx --download-hypre=1 >>>> [0]PETSC ERROR: >>>> ------------------------------------------------------------------------ >>>> [0]PETSC ERROR: MatPtAP() line 8166 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/mat/interface/matrix.c >>>> [0]PETSC ERROR: PCSetUp_MG() line 628 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/pc/impls/mg/mg.c >>>> [0]PETSC ERROR: PCSetUp() line 890 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/pc/interface/precon.c >>>> [0]PETSC ERROR: KSPSetUp() line 278 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/ksp/interface/itfunc.c >>>> [0]PETSC ERROR: KSPSolve() line 399 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/ksp/interface/itfunc.c >>>> [0]PETSC ERROR: PCApply_FieldSplit_Schur() line 807 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/pc/impls/fieldsplit/fieldsplit.c >>>> [0]PETSC ERROR: PCApply() line 442 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/pc/interface/precon.c >>>> [0]PETSC ERROR: KSP_PCApply() line 227 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/include/petsc-private/kspimpl.h >>>> [0]PETSC ERROR: KSPInitialResidual() line 64 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/ksp/interface/itres.c >>>> [0]PETSC ERROR: KSPSolve_GMRES() line 239 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/ksp/impls/gmres/gmres.c >>>> [0]PETSC ERROR: KSPSolve() line 441 in >>>> /home/bkhanal/Documents/softwares/petsc-3.4.2/src/ksp/ksp/interface/itfunc.c >>>> >>>> >>>> >>> >>> >>> -- >>> 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 >>> >> >> > > > -- > 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 >
