text: 
  static char help[] = "Tests MatIncreaseOverlap() and MatCreateSubmatrices() for the parallel case.\n\
  This example is similar to ex40.c; here the index sets used are random.\n\
  Input arguments are:\n\
    -f <input_file> : file to load.  For example see $PETSC_DIR/share/petsc/datafiles/matrices\n\
    -nd <size>      : > 0  no of domains per processor \n\
    -ov <overlap>   : >=0  amount of overlap between domains\n\n";
  
  #include <petscmat.h>
  
  int main(int argc,char **args)
  {
    PetscErrorCode ierr;
    PetscInt       nd = 2,ov=1,i,j,lsize,m,n,*idx,bs;
    PetscMPIInt    rank, size;
    PetscBool      flg;
    Mat            A,B,*submatA,*submatB;
    char           file[PETSC_MAX_PATH_LEN];
    PetscViewer    fd;
    IS             *is1,*is2;
    PetscRandom    r;
    PetscBool      test_unsorted = PETSC_FALSE;
    PetscScalar    rand;
  
    ierr = PetscInitialize(&argc,&args,(char*)0,help);if (ierr) return ierr;
    ierr = MPI_Comm_size(PETSC_COMM_WORLD,&size);CHKERRQ(ierr);
    ierr = MPI_Comm_rank(PETSC_COMM_WORLD,&rank);CHKERRQ(ierr);
    ierr = PetscOptionsGetString(NULL,NULL,"-f",file,sizeof(file),NULL);CHKERRQ(ierr);
    ierr = PetscOptionsGetInt(NULL,NULL,"-nd",&nd,NULL);CHKERRQ(ierr);
    ierr = PetscOptionsGetInt(NULL,NULL,"-ov",&ov,NULL);CHKERRQ(ierr);
    ierr = PetscOptionsGetBool(NULL,NULL,"-test_unsorted",&test_unsorted,NULL);CHKERRQ(ierr);
  
    /* Read matrix A and RHS */
    ierr = PetscViewerBinaryOpen(PETSC_COMM_WORLD,file,FILE_MODE_READ,&fd);CHKERRQ(ierr);
    ierr = MatCreate(PETSC_COMM_WORLD,&A);CHKERRQ(ierr);
    ierr = MatSetType(A,MATAIJ);CHKERRQ(ierr);
    ierr = MatSetFromOptions(A);CHKERRQ(ierr);
    ierr = MatLoad(A,fd);CHKERRQ(ierr);
    ierr = PetscViewerDestroy(&fd);CHKERRQ(ierr);
  
    /* Read the same matrix as a seq matrix B */
    ierr = PetscViewerBinaryOpen(PETSC_COMM_SELF,file,FILE_MODE_READ,&fd);CHKERRQ(ierr);
    ierr = MatCreate(PETSC_COMM_SELF,&B);CHKERRQ(ierr);
    ierr = MatSetType(B,MATSEQAIJ);CHKERRQ(ierr);
    ierr = MatSetFromOptions(B);CHKERRQ(ierr);
    ierr = MatLoad(B,fd);CHKERRQ(ierr);
    ierr = PetscViewerDestroy(&fd);CHKERRQ(ierr);
  
    ierr = MatGetBlockSize(A,&bs);CHKERRQ(ierr);
  
    /* Create the Random no generator */
    ierr = MatGetSize(A,&m,&n);CHKERRQ(ierr);
    ierr = PetscRandomCreate(PETSC_COMM_SELF,&r);CHKERRQ(ierr);
    ierr = PetscRandomSetFromOptions(r);CHKERRQ(ierr);
  
    /* Create the IS corresponding to subdomains */
    ierr = PetscMalloc1(nd,&is1);CHKERRQ(ierr);
    ierr = PetscMalloc1(nd,&is2);CHKERRQ(ierr);
    ierr = PetscMalloc1(m ,&idx);CHKERRQ(ierr);
    for (i = 0; i < m; i++) {idx[i] = i;CHKERRQ(ierr);}
  
    /* Create the random Index Sets */
    for (i=0; i<nd; i++) {
      /* Skip a few,so that the IS on different procs are diffeent*/
      for (j=0; j<rank; j++) {
        ierr = PetscRandomGetValue(r,&rand);CHKERRQ(ierr);
      }
      ierr  = PetscRandomGetValue(r,&rand);CHKERRQ(ierr);
      lsize = (PetscInt)(rand*(m/bs));
      /* shuffle */
      for (j=0; j<lsize; j++) {
        PetscInt k, swap, l;
  
        ierr   = PetscRandomGetValue(r,&rand);CHKERRQ(ierr);
        k      = j + (PetscInt)(rand*((m/bs)-j));
        for (l = 0; l < bs; l++) {
          swap        = idx[bs*j+l];
          idx[bs*j+l] = idx[bs*k+l];
          idx[bs*k+l] = swap;
        }
      }
      if (!test_unsorted) {ierr = PetscSortInt(lsize*bs,idx);CHKERRQ(ierr);}
      ierr = ISCreateGeneral(PETSC_COMM_SELF,lsize*bs,idx,PETSC_COPY_VALUES,is1+i);CHKERRQ(ierr);
      ierr = ISCreateGeneral(PETSC_COMM_SELF,lsize*bs,idx,PETSC_COPY_VALUES,is2+i);CHKERRQ(ierr);
      ierr = ISSetBlockSize(is1[i],bs);CHKERRQ(ierr);
      ierr = ISSetBlockSize(is2[i],bs);CHKERRQ(ierr);
    }
  
    if (!test_unsorted) {
      ierr = MatIncreaseOverlap(A,nd,is1,ov);CHKERRQ(ierr);
      ierr = MatIncreaseOverlap(B,nd,is2,ov);CHKERRQ(ierr);
  
      for (i=0; i<nd; ++i) {
        ierr = ISSort(is1[i]);CHKERRQ(ierr);
        ierr = ISSort(is2[i]);CHKERRQ(ierr);
      }
    }
  
    ierr = MatCreateSubMatrices(A,nd,is1,is1,MAT_INITIAL_MATRIX,&submatA);CHKERRQ(ierr);
    ierr = MatCreateSubMatrices(B,nd,is2,is2,MAT_INITIAL_MATRIX,&submatB);CHKERRQ(ierr);
  
    /* Now see if the serial and parallel case have the same answers */
    for (i=0; i<nd; ++i) {
      ierr = MatEqual(submatA[i],submatB[i],&flg);CHKERRQ(ierr);
      if (!flg) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_PLIB,"%D-th paralle submatA != seq submatB",i);
    }
  
    /* Free Allocated Memory */
    for (i=0; i<nd; ++i) {
      ierr = ISDestroy(&is1[i]);CHKERRQ(ierr);
      ierr = ISDestroy(&is2[i]);CHKERRQ(ierr);
    }
    ierr = MatDestroySubMatrices(nd,&submatA);CHKERRQ(ierr);
    ierr = MatDestroySubMatrices(nd,&submatB);CHKERRQ(ierr);
  
    ierr = PetscRandomDestroy(&r);CHKERRQ(ierr);
    ierr = PetscFree(is1);CHKERRQ(ierr);
    ierr = PetscFree(is2);CHKERRQ(ierr);
    ierr = MatDestroy(&A);CHKERRQ(ierr);
    ierr = MatDestroy(&B);CHKERRQ(ierr);
    ierr = PetscFree(idx);CHKERRQ(ierr);
    ierr = PetscFinalize();
    return ierr;
  }
  
  
  
  /*TEST
  
     build:
        requires: !complex
  
     test:
        nsize: 3
        requires: datafilespath double !define(PETSC_USE_64BIT_INDICES) !complex
        args: -f ${DATAFILESPATH}/matrices/arco1 -nd 5 -ov 2
  
     test:
        suffix: 2
        args: -f ${DATAFILESPATH}/matrices/arco1 -nd 8 -ov 2
        requires: datafilespath double !define(PETSC_USE_64BIT_INDICES) !complex
  
     test:
        suffix: unsorted_baij_mpi
        nsize: 3
        requires: datafilespath double !define(PETSC_USE_64BIT_INDICES) !complex
        args: -f ${DATAFILESPATH}/matrices/cfd.1.10 -nd 8 -mat_type baij -test_unsorted
  
     test:
        suffix: unsorted_baij_seq
        requires: datafilespath double !define(PETSC_USE_64BIT_INDICES) !complex
        args: -f ${DATAFILESPATH}/matrices/cfd.1.10 -nd 8 -mat_type baij -test_unsorted
  
     test:
        suffix: unsorted_mpi
        nsize: 3
        requires: datafilespath double !define(PETSC_USE_64BIT_INDICES) !complex
        args: -f ${DATAFILESPATH}/matrices/arco1 -nd 8 -test_unsorted
  
     test:
        suffix: unsorted_seq
        requires: datafilespath double !define(PETSC_USE_64BIT_INDICES) !complex
        args: -f ${DATAFILESPATH}/matrices/arco1 -nd 8 -test_unsorted
  
  TEST*/
  