[petsc-users] Convert matrix to 1-D array

[Hong]

Priyank:
The product C = A * B is a dense matrix in petsc mpidense format.
You should use MatDenseGetArray()
http://www.mcs.anl.gov/petsc/petsc-current/docs/manualpages/Mat/MatDenseGetArray.html

which gives 1D array of local entries of C.

I notice you are using petsc-3.3. Please update to the latest version of petsc.

Hong

> Hello,
>
>  I have a matrix generated from matrix matrix multiplication. I want that
> matrix to convert to 1 dimensional array. my code is as below
>
> #####################################################
> //Multiplication A * B (A is MPIAIJ & B is MPIDENSE)
> MatMatMult(A, B,  MAT_INITIAL_MATRIX,  PETSC_DEFAULT, &C);
> MatView(C,PETSC_VIEWER_STDOUT_WORLD);
> //Convert Matrix C to 1D vector h_C
> for(i = 0; i < m; i++)
> {
> for(j = 0; j < k; j++)
> {
> ierr = MatGetValues(C, 1, &i, 1, &j, &h_C[IDX2C(i,j,end1)]);CHKERRQ(ierr);
> }
> }
> //printArray(h_B, m, k, "h_B");
> printArray(h_C, m, k, "A * X0");
> #####################################################
> when I tried the routine MatGetValues() it shows some error as below
>
> #####################################################
> --------------------- Error Message ------------------------------------
> [1]PETSC ERROR: No support for this operation for this object type!
> [1]PETSC ERROR: Only local values currently supported!
> [1]PETSC ERROR:
> ------------------------------------------------------------------------
> [1]PETSC ERROR: Petsc Release Version 3.3.0, Patch 0, Tue Jun  5 14:20:42
> CDT 2012
> [1]PETSC ERROR: See docs/changes/index.html for recent updates.
> [1]PETSC ERROR: See docs/faq.html for hints about trouble shooting.
> [1]PETSC ERROR: See docs/index.html for manual pages.
> [1]PETSC ERROR:
> ------------------------------------------------------------------------
> [1]PETSC ERROR: ./blockCG_1 on a arch-linu named hpcd.cs.odu.edu by ppatel
> Tue Aug 19 12:29:41 2014
> [1]PETSC ERROR: Libraries linked from /export/software/petsc-3.3/lib
> [1]PETSC ERROR: Configure run at Wed Jun  6 16:29:21 2012
> [1]PETSC ERROR: Configure options --prefix=/export/software/petsc-3.3
> --download-f-blas-lapack=1
> [1]PETSC ERROR:
> ------------------------------------------------------------------------
> [1]PETSC ERROR: MatGetValues_MPIDense() line 180 in
> src/mat/impls/dense/mpi/mpidense.c
> [1]PETSC ERROR: MatGetValues() line 1602 in src/mat/interface/matrix.c
> [1]PETSC ERROR: main() line 343 in blockCG_1.c
> --------------------------------------------------------------------------
> MPI_ABORT was invoked on rank 1 in communicator MPI_COMM_WORLD
> with errorcode 56.
>
> NOTE: invoking MPI_ABORT causes Open MPI to kill all MPI processes.
> You may or may not see output from other processes, depending on
> exactly when Open MPI kills them.
> --------------------------------------------------------------------------
>
> #####################################################
>
> what is the efficient way to create a 1-D array from the PETSC matrix?