[petsc-users] How to access Vector data properly

[Matthew Knepley]

On Mon, Apr 9, 2018 at 1:15 PM, Songtao Chu <st.chu at outlook.com> wrote:

> Thank you for your correction.
> I rebuilt the code under Linux, the bug disappeared. It seems this is a
> bug of WSL.
>

Thanks,

    Matt


> ------------------------------
> *From:* Satish Balay <balay at mcs.anl.gov>
> *Sent:* Tuesday, April 10, 2018 0:20
> *To:* Songtao Chu
> *Cc:* Matthew Knepley; petsc-users at mcs.anl.gov
> *Subject:* Re: [petsc-users] How to access Vector data properly
>
> On Mon, 9 Apr 2018, Songtao Chu wrote:
>
> > static char help[] = "\n\n";
> > #include <petscdm.h>
> > #include <petscdmda.h>
> >
> >
> > int main(int argc,char **argv)
> > {
> >     PetscMPIInt     rank;
> >     PetscErrorCode  ierr;
> >     Vec             global,local,natural;
> >     DM              da;
> >     PetscReal       *val;
> >     PetscInt        i,x,xm;
> >
> >
> >     ierr = PetscInitialize(&argc,&argv,(char*)0,help);if (ierr) return
> ierr;
> >     ierr = MPI_Comm_rank(PETSC_COMM_WORLD,&rank);CHKERRQ(ierr);
> >
> >     ierr = DMDACreate1d(PETSC_COMM_WORLD,DM_BOUNDARY_NONE,5,1,1,NULL,&
> da);CHKERRQ(ierr);
> >     ierr = DMSetUp(da);CHKERRQ(ierr);
> >     ierr = DMCreateGlobalVector(da,&global);CHKERRQ(ierr);
> >
> >     ierr = DMDAGetCorners(da,&x,NULL,NULL,&xm,NULL,NULL);CHKERRQ(ierr);
> >     ierr = DMDAVecGetArray(da, global, &val);CHKERRQ(ierr);
> >     ierr = PetscSynchronizedPrintf(PETSC_COMM_SELF, "Rank=%d\n",
> rank);CHKERRQ(ierr);
>
> Shouldn't this call be removed? Nothing of substance is printed here.
>
> >     for (i = x; i < x + xm; ++i) {
> >         val[i] = i;
> >     }
> >     ierr = DMDAVecRestoreArray(da, global, &val);CHKERRQ(ierr);
> >
> >     VecView(global,PETSC_VIEWER_STDOUT_WORLD);
> >
> >     ierr = DMDAGetCorners(da,&x,NULL,NULL,&xm,NULL,NULL);CHKERRQ(ierr);
> >     ierr = DMDAVecGetArray(da, global, &val);CHKERRQ(ierr);
> >     ierr = PetscSynchronizedPrintf(PETSC_COMM_SELF, "Rank=%d\n",
> rank);CHKERRQ(ierr);
>
> Shouldn't this be on PETSC_COMM_WORLD?
>
> >     for (i = x; i < x + xm; ++i) {
> >         ierr = PetscSynchronizedPrintf(PETSC_COMM_SELF, "%4.f ",
> val[i]);CHKERRQ(ierr);
>
> Again PETSC_COMM_WORLD?
>
>
> >     }
> >     ierr = DMDAVecRestoreArray(da, global, &val);CHKERRQ(ierr);
> >     PetscSynchronizedFlush(PETSC_COMM_SELF, PETSC_STDOUT);
> >
> >     ierr = PetscFinalize();
> >     return ierr;
> > }
>
> Attaching the fixed code.
>
> Satish
> -------
> balay at asterix /home/balay/download-pine
> $ ./ex1
> Vec Object: 1 MPI processes
>   type: seq
> 0.
> 1.
> 2.
> 3.
> 4.
> Rank=0
>    0    1    2    3    4
> balay at asterix /home/balay/download-pine
> $ mpiexec -n 2 ./ex1
> Vec Object: 2 MPI processes
>   type: mpi
> Process [0]
> 0.
> 1.
> 2.
> Process [1]
> 3.
> 4.
> Rank=0
>    0    1    2
> Rank=1
>    3    4
> balay at asterix /home/balay/download-pine
> $ mpiexec -n 3 ./ex1
> Vec Object: 3 MPI processes
>   type: mpi
> Process [0]
> 0.
> 1.
> Process [1]
> 2.
> 3.
> Process [2]
> 4.
> Rank=0
>    0    1
> Rank=1
>    2    3
> Rank=2
>    4
> balay at asterix /home/balay/download-pine
> $
>



-- 
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

https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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