[petsc-users] (no subject)

[amlan barua]

Hi Barry,
I wrote the following piece according to your suggestions. Currently it
does nothing but creates a vector with 1 at 1th position, 2 at 2th and so
on. But I made it serial, i.e. (n+1)th place is computed using the value of
nth place. My question, did I do it correctly, i.e. is it safe or results
may change depending on problem size? This is much faster than
VecSetValues, I believe the communication is minimum here because I take
the advantage of ghost points.
Amlan

PetscInitialize(&argc,&argv,(char *)0,help);
    ierr = MPI_Comm_size(PETSC_COMM_WORLD, &size); CHKERRQ(ierr);
    ierr = MPI_Comm_rank(PETSC_COMM_WORLD, &rank); CHKERRQ(ierr);
    ierr =
DMDACreate1d(PETSC_COMM_WORLD,DMDA_BOUNDARY_NONE,size*5,1,1,PETSC_NULL,&da);
CHKERRQ(ierr);
    ierr = DMCreateGlobalVector(da,&vec); CHKERRQ(ierr);
    ierr = VecSet(vec,1.00);
    ierr = DMCreateLocalVector(da,&local);
    ierr = DMDAGetLocalInfo(da,&info);
    ierr = DMDAVecGetArray(da,vec,&arr);
    ierr = DMDAVecGetArray(da,local,&array);
    temp = 1;
    for (j=0;j<size;j++) {
       ierr = DMGlobalToLocalBegin(da,vec,INSERT_VALUES,local);
CHKERRQ(ierr);
       ierr = DMGlobalToLocalEnd(da,vec,INSERT_VALUES,local);
CHKERRQ(ierr);
       if (rank==j) {
       for (i=info.xs;i<info.xs+info.xm;i++) {
          if ((!i)==0) {
            array[i] = array[i] + array[i-1];
            arr[i] = array[i];
            }
          }
       }
       }
    ierr = DMDAVecRestoreArray(da,local,&array);
    ierr = DMDAVecRestoreArray(da,vec,&arr);
    ierr = VecView(vec,PETSC_VIEWER_STDOUT_WORLD);
    PetscFinalize();
    return 0;



On Thu, Dec 27, 2012 at 10:40 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
> On Dec 27, 2012, at 10:34 AM, amlan barua <abarua at iit.edu> wrote:
>
> > I think I can use VecSetValues, is that right?
>
>    Yes you could do that. But since you are using a DMDA you could also
> use DMGetLocalVector(), DMGlobalToLocalBegin/End() followed by
> DMDAVecGetArray() to access the ghost values.
>
>    Barry
>
> > Amlan
> >
> >
> > On Thu, Dec 27, 2012 at 9:04 AM, amlan barua <abarua at iit.edu> wrote:
> > Hi Barry,
> > Is this scattering a very costly operation? I have to compute x[i] =
> f(x[i-1]) where f is known. Since this operation is strictly sequential, I
> thought of gathering the entire vector on processor 0, do the sequential
> operation there and scatter the result back. However this is unnecessary
> because I only need the bordering x[i] values. What can be a better way?
> > Amlan
> >
> >
> > On Thu, Dec 27, 2012 at 8:18 AM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >   ierr = DMDACreateNaturalVector(da,&natural);CHKERRQ(ierr);
> >     ierr =
> DMDAGlobalToNaturalBegin(da,xin,INSERT_VALUES,natural);CHKERRQ(ierr);
> >     ierr =
> DMDAGlobalToNaturalEnd(da,xin,INSERT_VALUES,natural);CHKERRQ(ierr);
> >
> > Now do VecScatterCreateToZero() from natural and the vector will be in
> the natural ordering on process zero with the dof interlaced.
> >
> >
> >    Barry
> >
> > On Dec 27, 2012, at 12:22 AM, amlan barua <abarua at iit.edu> wrote:
> >
> > > Hi,
> > > Is there an analogue of VecScatterCreateToZero for DA vectors? The
> DMDA object has more than one degrees of freedom.
> > > If there isn't any, should I use an IS object to do the scattering?
> > > Amlan
> >
> >
> >
>
>
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