[petsc-users] Some help for partitioning a vector

[ehsan sadrfaridpour]

Thanks a lot, sorry I didn't catch the SELF from my sequential version.

Best,
Ehsan

On Tue, Jun 28, 2016 at 12:22 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Only parallel vectors can be multiplied with parallel matrices and the
> vector and matrix must exist on the same MPI communicator. In your case you
> are trying to multiple a sequential vector by a parallel matrix.  You
> should use VecCreateMPI(PETSC_COMM_WORLD, PETSC_DECIDE, size_,&vol_);
>
>                                                                ^^^^^^
>                       use PETSC_COMM_WORLD or the communicator you used in
> creating the matrix, don't use PETSC_COMM_SELF
>
>
> > On Jun 28, 2016, at 9:14 AM, ehsan sadrfaridpour <it.sadr at gmail.com>
> wrote:
> >
> > Hi,
> > Sorry for long email. My questions are in the bottom.
> >
> > I try to use MatMult to multiply a vector to a matrix but I face below
> problem.
> > [0]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> > [0]PETSC ERROR: Nonconforming object sizes
> > [0]PETSC ERROR: Incompatible partition of A (20) and xx (40)
> > [0]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> > [1]PETSC ERROR: --------------------- Error Message
> --------------------------------------------------------------
> > [1]PETSC ERROR: Nonconforming object sizes
> > [1]PETSC ERROR: Incompatible partition of A (20) and xx (40)
> > [1]PETSC ERROR: See http://www.mcs.anl.gov/petsc/documentation/faq.html
> for trouble shooting.
> > [1]PETSC ERROR: Petsc Release Version 3.6.3, unknown
> >
> > I use 2 process for this. I check the local ranges with
> VecGetOwnershipRange and MatGetOwnershipRange commands and they reveal that
> the matrix is distributed between processes while the vector is exist
> completely on both processes.
> > in rank:1, vector start:0, end:40, matrix start:20, end:40
> > in rank:0, vector start:0, end:40, matrix start:0, end:20
> >
> > I created the vector "vol_" using below commands.
> >    Vec vol_;
> >     VecCreateMPI(PETSC_COMM_SELF, PETSC_DECIDE, size_,&vol_);
> >     VecSet(vol_,val);           //Sets all components of a vector to a
> single scalar value.
> >     VecAssemblyBegin(vol_);
> >     VecAssemblyEnd(vol_);
> >
> > My questions:
> > A- What should I do differently to create a scattered vector in the
> first place?
> > B- If my vector initialization is ok, what should I do now to scatter
> the vector among the processes?
> > I saw the VecScatter function, but I am not sure how to use it, if it is
> the right function.
> >
> > Best,
> > Ehsan
> >
>
>
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