[petsc-users] KSPSetDM problem

[Barry Smith]

   Since you set the DM inactive   the PCSetUp_MG() has no code to compute the coarser grid operators. You need to either 

1) provide a DMKSPSetComputeOperators () function that will compute the operator for all levels or

2) run with -pc_mg_galerkin to have the coarse grid operators computed by multiplying the fine grid operator by the restriction/interpolation.

   Barry

On Nov 14, 2013, at 7:49 PM, Michele Rosso <mrosso at uci.edu> wrote:

> Hi,
> 
> I am  solving a Poisson equation (cell-centered discretization) with multigrid.
> I am using a 2D version of ksp/ksp/examples/tutorials/ex34.c as a reference. 
> The following code performs the same calculations as ex34:
> 
>   call PetscInitialize(PETSC_NULL_CHARACTER,ierr)
> 
>     call DMDACreate2d(PETSC_COMM_WORLD, DMDA_BOUNDARY_NONE, DMDA_BOUNDARY_NONE,&
>          & DMDA_STENCIL_STAR, 16, 16, PETSC_DECIDE, PETSC_DECIDE, &
>          & 1, 1, PETSC_NULL_INTEGER, PETSC_NULL_INTEGER,da,ierr)
>     call DMDASetInterpolationType(da, DMDA_Q0, ierr);
>     call DMCreateGlobalVector(da,b,ierr)
>     call create_rhs(da,b)
>     call DMCreateMatrix(da,'aij',A,ierr)
>     call create_matrix(da,A)
>     call VecDuplicate(b,x,ierr)
>     
>     ! Create solver
>     call KSPCreate(PETSC_COMM_WORLD,solver,ierr)  
>     call KSPSetDM(solver,da,ierr)
>     call KSPSetDMActive(solver,PETSC_FALSE,ierr)
>     call KSPSetOperators(solver,A,A,SAME_NONZERO_PATTERN,ierr)
>     call KSPSetType(solver,'cg',ierr)
>     call KSPSetNormType(solver,KSP_NORM_UNPRECONDITIONED,ierr)
>     call KSPSetFromOptions(solver,ierr)
>     call KSPSolve(solver,b,x,ierr)    
>     
>     rerr = error(da,x)
>     
>     call PetscFinalize(ierr)
> 
> 
> Both ex34 and my code produce exactly the same results except when I run with 
> 
> -ksp_view -ksp_monitor_true_residual -ksp_converged_reason -ksp_type cg -pc_type mg -pc_mg_levels 4 
> 
> In this case my code results in the following error, despite KSPSetDMActive is used after KSPSetDM:
> 
> [0]PETSC ERROR: --------------------- Error Message ------------------------------------
> [0]PETSC ERROR: Object is in wrong state!
> [0]PETSC ERROR: You called KSPSetDM() but did not use DMKSPSetComputeOperators() or KSPSetDMActive(dm,PETSC_FALSE);!
> [0]PETSC ERROR: ------------------------------------------------------------------------
> [0]PETSC ERROR: Petsc Release Version 3.4.3, Oct, 15, 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: ./test on a linux-gnu-dbg named enterprise-A by mic Thu Nov 14 17:38:23 2013
> [0]PETSC ERROR: Libraries linked from /opt/petsc/petsc-3.4.3/linux-gnu-dbg/lib
> [0]PETSC ERROR: Configure run at Tue Oct 29 22:43:45 2013
> [0]PETSC ERROR: Configure options --known-mpi-shared="0 " --known-memcmp-ok  --with-debugging="1 " --with-fortran-datatypes --with-shared-libraries=0 --with-dynamic-loading=0 --with-mpi-compilers="1 " --download-blacs="1 " --download-superlu_dist="1 " --download-metis="1 " --download-parmetis="1 " --download-ml=1 PETSC_ARCH=linux-gnu-dbg
> [0]PETSC ERROR: ------------------------------------------------------------------------
> [0]PETSC ERROR: KSPSetUp() line 230 in /opt/petsc/petsc-3.4.3/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: PCSetUp_MG() line 730 in /opt/petsc/petsc-3.4.3/src/ksp/pc/impls/mg/mg.c
> [0]PETSC ERROR: PCSetUp() line 890 in /opt/petsc/petsc-3.4.3/src/ksp/pc/interface/precon.c
> [0]PETSC ERROR: KSPSetUp() line 278 in /opt/petsc/petsc-3.4.3/src/ksp/ksp/interface/itfunc.c
> [0]PETSC ERROR: KSPSolve() line 399 in /opt/petsc/petsc-3.4.3/src/ksp/ksp/interface/itfunc.c
> 
> 
> Am I missing anything?
> Thank you,
> 
> Michele
> 
> 
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>