[petsc-users] How to have a local copy (sequential) of a parallel matrix

[ehsan sadrfaridpour]

Thanks, it works!

On Wed, Jun 29, 2016 at 4:31 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   On all other processes don't pass in 1 pass  in 0 since all other
> processes want 0 sub matrices
>
>
> > On Jun 29, 2016, at 3:24 PM, ehsan sadrfaridpour <it.sadr at gmail.com>
> wrote:
> >
> > Thanks, the IS problem is solved.
> > But now I have another problem to compile the code.
> >
> > I use below code:
> > Mat m_WA_nt_local;
> >     MatCreateSeqAIJ(PETSC_COMM_SELF,num_points,num_points,
> Config_params::getInstance()->get_pre_init_loader_matrix(), NULL,
> &m_WA_nt_local);
> >     IS set;
> >     if(rank ==0){
> >         ISCreateStride(PETSC_COMM_SELF, num_points, 0, 1, &set);
> >         ISView(set, PETSC_VIEWER_STDOUT_SELF);
> >     }
> >     MatGetSubMatrices(m_WA_norm_T, 1, &set, &set, MAT_INITIAL_MATRIX,
> &m_WA_nt_local);
> >
> > The error I get is :
> > error: cannot convert ‘_p_Mat**’ to ‘_p_Mat***’ for argument ‘6’ to
> ‘PetscErrorCode MatGetSubMatrices(Mat, PetscInt, _p_IS* const*, _p_IS*
> const*, MatReuse, _p_Mat***)’
> >      MatGetSubMatrices(m_WA_norm_T, 1, &set, &set, MAT_INITIAL_MATRIX,
> &m_WA_nt_local);
> >
> >
> > I tried to go around it by define a array of Matrices using "Mat *
> m_WA_nt_local"
> > So, the first 2 lines changed to below and I can compile the code.
> > Mat * m_WA_nt_local;
> >     MatCreateSeqAIJ(PETSC_COMM_SELF,num_points,num_points,
> Config_params::getInstance()->get_pre_init_loader_matrix(), NULL,
> m_WA_nt_local);
> >
> >
> >
> > However, I get errors like below when I run the code with 2 mpi process.
> >  --------------------- Error Message
> --------------------------------------------------------------
> > [1]PETSC ERROR: Invalid argument
> > [1]PETSC ERROR: Wrong type of object: Parameter # 3
> > [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
> > [1]PETSC ERROR: ut_main on a linux-cxx-debug named grappelli by esfp Wed
> Jun 29 16:21:04 2016
> > [1]PETSC ERROR: Configure options PETSC_ARCH=linux-cxx-debug
> --with-cc=gcc --with-cxx=g++ --with-clanguage=c++ --with-gnu-compilers=1
> --with-mpi-compilers=1 --with-debugging=1 --with-shared-libraries=1
> --download-openmpi=1 --download-f2cblaslapack --download-superlu_dist=1
> --download-superlu=1 --download-metis=1 --download-parmetis=1
> --download-blacs=1 --with-hdf5 --with-hdf5-dir=/usr/local/hdf5/
> > [1]PETSC ERROR: #1 MatGetSubMatrices() line 6605 in
> /home/esfp/tools/libraries/petsc/src/mat/interface/matrix.c
> >
> >
> > I think I need to do something for other processes, but I don't know
> what I need to do.
> >
> > Best,
> > Ehsan
> >
> >
> >
> > On Wed, Jun 29, 2016 at 4:03 PM, Dave May <dave.mayhem23 at gmail.com>
> wrote:
> >
> >
> > On Wednesday, 29 June 2016, ehsan sadrfaridpour <it.sadr at gmail.com>
> wrote:
> > I faced the below error during compiling my code for using
> MatGetSubMatrices.
> >
> > error: cannot convert ‘IS {aka _p_IS*}’ to ‘_p_IS* const*’ for argument
> ‘3’ to ‘PetscErrorCode MatGetSubMatrices(Mat, PetscInt, _p_IS* const*,
> _p_IS* const*, MatReuse, _p_Mat***)’
> >          MatGetSubMatrices(m_WA_norm_T, 1, set, set, MAT_INITIAL_MATRIX,
> &m_local_W);
> >
> > My code :
> > PetscMPIInt    rank;
> > MPI_Comm_rank(PETSC_COMM_WORLD, &rank);
> >
> > if(rank ==0){
> >         Mat m_local_W;
> >         MatCreateSeqAIJ(PETSC_COMM_SELF,num_points,num_points, num_nz,
> NULL,&m_local_W);// try to reserve space for only number of final non zero
> entries for each fine node (e.g. 4)
> >         IS set;
> >         ISCreateStride(PETSC_COMM_SELF, num_points, 0, 1, &set_row);
> >         MatGetSubMatrices(m_WA_norm_T, 1, set_row, set_col,
> MAT_INITIAL_MATRIX, &m_local_W);
> >
> >     }
> >
> > I followed below example:
> >
> http://www.mcs.anl.gov/petsc/petsc-current/src/vec/is/is/examples/tutorials/ex2.c.html
> >
> > This code won't work in parallel.
> > The man page says this function is collective on Mat. You need to move
> the call to MatGetSubMatrices outside of the if(rank==0) loop.
> >
> >
> >
> >
> >
> >
> >
> > On Wed, Jun 29, 2016 at 3:19 PM, ehsan sadrfaridpour <it.sadr at gmail.com>
> wrote:
> > Thanks a lot for great support.
> >
> > On Wed, Jun 29, 2016 at 3:11 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:
> >
> >    MatGetSubmatrices() just have the first process request all the rows
> and columns and the others request none. You can use ISCreateStride() to
> create the ISs without having to make an array of all the indices.
> >
> >
> > > On Jun 29, 2016, at 1:43 PM, ehsan sadrfaridpour <it.sadr at gmail.com>
> wrote:
> > >
> > > Hi,
> > >
> > > I need to have access to most of elements of a parallel MPIAIJ matrix
> only from 1 process (rank 0).
> > > I tried to copy or duplicate it to SEQAIJ, but I faced problems.
> > >
> > > How can I have a local copy of a matrix which is distributed on
> multiple process? I don't want to update the matrix, and the read-only
> version of it would be enough.
> > >
> > > Best,
> > > Ehsan
> > >
> > >
> >
> >
> >
> >
>
>
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