static char help[] = "Testing MatCreateMPIMatConcatenateSeqMat().\n\n";

#include <petscmat.h>
int main(int argc,char **argv)
{
  Mat            seqmat,mpimat;
  PetscMPIInt    rank;
  PetscScalar    value[3],*vals;
  PetscInt       i,col[3],n=5,bs=1;

  PetscFunctionBeginUser;
  PetscCall(PetscInitialize(&argc,&argv,(char*)0,help));
  PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD,&rank));
  PetscCall(PetscOptionsGetInt(NULL,NULL,"-bs",&bs,NULL));

  /* Create seqaij matrices of size (n+rank) by n */
  PetscCall(MatCreate(PETSC_COMM_SELF,&seqmat));
  PetscCall(MatSetSizes(seqmat,(n+rank)*bs,PETSC_DECIDE,PETSC_DECIDE,n*bs));
  PetscCall(MatSetFromOptions(seqmat));
  PetscCall(MatSeqAIJSetPreallocation(seqmat,3*bs,NULL));
  PetscCall(MatSeqBAIJSetPreallocation(seqmat,bs,3,NULL));

  if (bs == 1) {
    value[0] = -1.0; value[1] = 2.0; value[2] = -1.0;
    for (i=1; i<n-1; i++) {
      col[0] = i-1; col[1] = i; col[2] = i+1;
      PetscCall(MatSetValues(seqmat,1,&i,3,col,value,INSERT_VALUES));
    }
    i = n - 1; col[0] = n - 2; col[1] = n - 1;
    PetscCall(MatSetValues(seqmat,1,&i,2,col,value,INSERT_VALUES));

    i = 0; col[0] = 0; col[1] = 1; value[0] = 2.0; value[1] = -1.0;
    PetscCall(MatSetValues(seqmat,1,&i,2,col,value,INSERT_VALUES));
  } else {
    PetscInt *rows,*cols,j;
    PetscCall(PetscMalloc3(bs*bs,&vals,bs,&rows,bs,&cols));
    /* diagonal blocks */
    for (i=0; i<bs*bs; i++) vals[i] = 2.0;
    for (i=0; i<n*bs; i+=bs) {
      for (j=0; j<bs; j++) {rows[j] = i+j; cols[j] = i+j;}
      PetscCall(MatSetValues(seqmat,bs,rows,bs,cols,vals,INSERT_VALUES));
    }
    /* off-diagonal blocks */
    for (i=0; i<bs*bs; i++) vals[i] = -1.0;
    for (i=0; i<(n-1)*bs; i+=bs) {
      for (j=0; j<bs; j++) {rows[j] = i+j; cols[j] = i+bs+j;}
      PetscCall(MatSetValues(seqmat,bs,rows,bs,cols,vals,INSERT_VALUES));
    }

    PetscCall(PetscFree3(vals,rows,cols));
  }
  PetscCall(MatAssemblyBegin(seqmat,MAT_FINAL_ASSEMBLY));
  PetscCall(MatAssemblyEnd(seqmat,MAT_FINAL_ASSEMBLY));
  if (rank == 0) {
    PetscCall(PetscPrintf(PETSC_COMM_SELF,"[%d] seqmat:\n",rank));
    PetscCall(MatView(seqmat,PETSC_VIEWER_STDOUT_SELF));
  }

  PetscCall(MatCreateMPIMatConcatenateSeqMat(PETSC_COMM_WORLD,seqmat,PETSC_DECIDE,MAT_INITIAL_MATRIX,&mpimat));
  PetscCall(MatCreateMPIMatConcatenateSeqMat(PETSC_COMM_WORLD,seqmat,PETSC_DECIDE,MAT_REUSE_MATRIX,&mpimat));
  PetscCall(MatView(mpimat,PETSC_VIEWER_STDOUT_WORLD));

  PetscCall(MatDestroy(&seqmat));
  PetscCall(MatDestroy(&mpimat));
  PetscCall(PetscFinalize());
  return 0;
}

/*TEST

   test:
      nsize: 3

   test:
      suffix: 2
      nsize: 3
      args: -mat_type baij

   test:
      suffix: 3
      nsize: 3
      args: -mat_type baij -bs 2

TEST*/