[petsc-users] general VecScatter from MPI to MPI

[Barry Smith]

  Ethan,

   It is perfectly possible to map from one global MPI vector to another global MPI vector. The vectors can be different or the same sizes and have different or the same layouts. 

   It is just not possible to use DEFAULT is in the from and two positions at the same time. Reason: if you don't provide either it doesn't have a way of generating both that are compatible with each other. I will add an error check for that case.  You should just generate the IS's that you need.

   Ignore Matt's ravings, you don't need to wrapping nothing in no SeqVec to scatter from MPI to MPI. Just provide the ISs.


   Barry


On Feb 17, 2011, at 10:06 AM, Ethan Coon wrote:

> So I thought I understood how VecScatters worked, but apparently not.
> Is it possible to create a general VecScatter from an arbitrarily
> partitioned (MPI) Vec to another arbitrarily partitioned (MPI) Vec with
> the same global sizes (or same global IS sizes) but different local
> sizes?  Shouldn't this just be a matter of relying upon the implied
> LocalToGlobalMapping?
> 
> See below snippet (and its errors):
> 
> Ethan
> 
> 
> 
> Vec vA
> Vec vB
> VecScatter scatter_AB
> 
> PetscInt np
> PetscInt rank
> PetscErrorCode ierr
> 
> if (rank.eq.0) np = 3
> if (rank.eq.1) np = 1
> 
> call VecCreateMPI(PETSC_COMM_WORLD, 2, PETSC_DETERMINE, vA, ierr)
> call VecCreateMPI(PETSC_COMM_WORLD, np, PETSC_DETERMINE, vB, ierr)
> 
> call VecScatterCreate(vA, PETSC_NULL_OBJECT, vB, PETSC_NULL_OBJECT, 
> 	scatter_AB, ierr)
> 
> ...
> 
> $> mpiexec -n 2 ./test
> 
> [0]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [0]PETSC ERROR: Nonconforming object sizes!
> [0]PETSC ERROR: Local scatter sizes don't match!
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [1]PETSC ERROR: --------------------- Error Message
> ------------------------------------
> [1]PETSC ERROR: Nonconforming object sizes!
> [1]PETSC ERROR: Local scatter sizes don't match!
> [0]PETSC ERROR: Petsc Development HG revision:
> 5dbe1264252fb9cb5d8e033d620d18f7b0e9111f  HG Date: Fri Feb 11 15:44:04
> 2011 -0600
> [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 named tama1 by ecoon Thu Feb 17
> 08:14:57 2011
> [0]PETSC ERROR: Libraries linked
> from /packages/petsc/petsc-dev3.0-mpich2-local-gcc-4.3.3/debug-shared/lib
> [0]PETSC ERROR: Configure run at Fri Feb 11 16:15:14 2011
> [0]PETSC ERROR: Configure options --with-debugging=1
> --prefix=/packages/petsc/petsc-dev3.0-mpich2-local-gcc-4.3.3/debug-shared --download-mpich=1 --download-ml=1 --download-umfpack=1 --with-blas-lapack-dir=/usr/lib --download-parmetis=yes PETSC_ARCH=linux-gnu-c-debug-shared --with-clanguage=c --download-hypre=1 --with-shared-libraries=1 --download-hdf5=1
> [0]PETSC ERROR:
> ------------------------------------------------------------------------
> [0]PETSC ERROR: VecScatterCreate() line 1432 in
> src/vec/vec/utils/vscat.c
> application called MPI_Abort(MPI_COMM_WORLD, 60) - process 0
> [cli_0]: aborting job:
> application called MPI_Abort(MPI_COMM_WORLD, 60) - process 0
> [1]PETSC ERROR: APPLICATION TERMINATED WITH THE EXIT STRING: Hangup
> (signal 1)
> 
> 
> 
> 
> -- 
> ------------------------------------
> Ethan Coon
> Post-Doctoral Researcher
> Applied Mathematics - T-5
> Los Alamos National Laboratory
> 505-665-8289
> 
> http://www.ldeo.columbia.edu/~ecoon/
> ------------------------------------
>