xref: /petsc/src/mat/impls/aij/seq/bas/spbas.c (revision 5fd668637986a8d8518383a9159eebc368e1d5b4)

#include <../src/mat/impls/aij/seq/aij.h>
#include <../src/mat/impls/aij/seq/bas/spbas.h>

/*MC
  MATSOLVERBAS -  Provides ICC(k) with drop tolerance

  Works with MATAIJ  matrices

  Options Database Keys:
+ -pc_factor_levels <l>
- -pc_factor_drop_tolerance

  Level: beginner

   Contributed by: Bas van 't Hof

.seealso: PCFactorSetMatSolverPackage(), MatSolverPackage, PCFactorSetLevels(), PCFactorSetDropTolerance()

M*/

/*
  spbas_memory_requirement:
    Calculate the number of bytes needed to store tha matrix
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_memory_requirement"
long int spbas_memory_requirement(spbas_matrix matrix)
{
  long int memreq = 6 * sizeof(PetscInt)  + /* nrows, ncols, nnz, n_alloc_icol,
                                               n_alloc_val, col_idx_type */
    sizeof(PetscBool)                     + /* block_data */
    sizeof(PetscScalar**)                 + /* values */
    sizeof(PetscScalar*)                  + /* alloc_val */
    2 * sizeof(int**)                     + /* icols, icols0 */
    2 * sizeof(PetscInt*)                 + /* row_nnz, alloc_icol */
    matrix.nrows * sizeof(PetscInt)       + /* row_nnz[*] */
    matrix.nrows * sizeof(PetscInt*);       /* icols[*] */

  /* icol0[*] */
  if (matrix.col_idx_type == SPBAS_OFFSET_ARRAY) { memreq += matrix.nrows * sizeof(PetscInt); }

  /* icols[*][*] */
  if (matrix.block_data) { memreq += matrix.n_alloc_icol * sizeof(PetscInt); }
  else { memreq += matrix.nnz * sizeof(PetscInt); }

  if (matrix.values) {
    memreq += matrix.nrows * sizeof(PetscScalar*); /* values[*] */
    /* values[*][*] */
      if (matrix.block_data) { memreq += matrix.n_alloc_val  * sizeof(PetscScalar); }
      else { memreq += matrix.nnz * sizeof(PetscScalar); }
  }
  return memreq;
}

/*
  spbas_allocate_pattern:
    allocate the pattern arrays row_nnz, icols and optionally values
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_allocate_pattern"
PetscErrorCode spbas_allocate_pattern(spbas_matrix * result, PetscBool  do_values)
{
  PetscErrorCode ierr;
  PetscInt       nrows = result->nrows;
  PetscInt       col_idx_type = result->col_idx_type;

  PetscFunctionBegin;
  /* Allocate sparseness pattern */
  ierr = PetscMalloc(nrows*sizeof(PetscInt),&result->row_nnz);CHKERRQ(ierr);
  ierr = PetscMalloc(nrows*sizeof(PetscInt*),&result->icols);CHKERRQ(ierr);

  /* If offsets are given wrt an array, create array */
  if (col_idx_type == SPBAS_OFFSET_ARRAY) {
    ierr = PetscMalloc(nrows*sizeof(PetscInt),&result->icol0);CHKERRQ(ierr);
  } else  {
    result->icol0 = PETSC_NULL;
  }

  /* If values are given, allocate values array */
  if (do_values)  {
    ierr = PetscMalloc(nrows*sizeof(PetscScalar*),&result->values);CHKERRQ(ierr);
  } else {
    result->values = PETSC_NULL;
  }
  PetscFunctionReturn(0);
}

/*
spbas_allocate_data:
   in case of block_data:
       Allocate the data arrays alloc_icol and optionally alloc_val,
       set appropriate pointers from icols and values;
   in case of !block_data:
       Allocate the arrays icols[i] and optionally values[i]
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_allocate_data"
PetscErrorCode spbas_allocate_data(spbas_matrix * result)
{
  PetscInt       i;
  PetscInt       nnz   = result->nnz;
  PetscInt       nrows = result->nrows;
  PetscInt       r_nnz;
  PetscErrorCode ierr;
  PetscBool      do_values = (result->values != PETSC_NULL) ? PETSC_TRUE : PETSC_FALSE;
  PetscBool      block_data = result->block_data;

  PetscFunctionBegin;
  if (block_data) {
    /* Allocate the column number array and point to it */
    result->n_alloc_icol = nnz;
    ierr = PetscMalloc(nnz*sizeof(PetscInt), &result->alloc_icol);CHKERRQ(ierr);
    result->icols[0]= result->alloc_icol;
    for (i=1; i<nrows; i++)  {
      result->icols[i] = result->icols[i-1] + result->row_nnz[i-1];
    }

    /* Allocate the value array and point to it */
    if (do_values)  {
      result->n_alloc_val= nnz;
      ierr = PetscMalloc(nnz*sizeof(PetscScalar), &result->alloc_val);CHKERRQ(ierr);
      result->values[0]= result->alloc_val;
      for (i=1; i<nrows; i++) {
        result->values[i] = result->values[i-1] + result->row_nnz[i-1];
      }
    }
  } else {
    for (i=0; i<nrows; i++)   {
      r_nnz = result->row_nnz[i];
      ierr = PetscMalloc(r_nnz*sizeof(PetscInt), &result->icols[i]);CHKERRQ(ierr);
    }
    if (do_values) {
      for (i=0; i<nrows; i++)  {
        r_nnz = result->row_nnz[i];
        ierr = PetscMalloc(r_nnz*sizeof(PetscScalar), &result->values[i]);CHKERRQ(ierr);
      }
    }
  }
  PetscFunctionReturn(0);
}

/*
  spbas_row_order_icol
     determine if row i1 should come
       + before row i2 in the sorted rows (return -1),
       + after (return 1)
       + is identical (return 0).
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_row_order_icol"
int spbas_row_order_icol(PetscInt i1, PetscInt i2, PetscInt *irow_in, PetscInt *icol_in,PetscInt col_idx_type)
{
  PetscInt j;
  PetscInt nnz1 = irow_in[i1+1] - irow_in[i1];
  PetscInt nnz2 = irow_in[i2+1] - irow_in[i2];
  PetscInt * icol1 = &icol_in[irow_in[i1]];
  PetscInt * icol2 = &icol_in[irow_in[i2]];

  if (nnz1<nnz2) {return -1;}
  if (nnz1>nnz2) {return 1;}

  if (col_idx_type == SPBAS_COLUMN_NUMBERS) {
    for (j=0; j<nnz1; j++) {
      if (icol1[j]< icol2[j]) {return -1;}
      if (icol1[j]> icol2[j]) {return 1;}
    }
  } else if (col_idx_type == SPBAS_DIAGONAL_OFFSETS) {
    for (j=0; j<nnz1; j++) {
      if (icol1[j]-i1< icol2[j]-i2) {return -1;}
      if (icol1[j]-i1> icol2[j]-i2) {return 1;}
    }
  } else if (col_idx_type == SPBAS_OFFSET_ARRAY) {
    for (j=1; j<nnz1; j++) {
      if (icol1[j]-icol1[0] < icol2[j]-icol2[0]) {return -1;}
      if (icol1[j]-icol1[0] > icol2[j]-icol2[0]) {return 1;}
    }
  }
  return 0;
}

/*
  spbas_mergesort_icols:
    return a sorting of the rows in which identical sparseness patterns are
    next to each other
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_mergesort_icols"
PetscErrorCode spbas_mergesort_icols(PetscInt nrows, PetscInt * irow_in, PetscInt * icol_in,PetscInt col_idx_type, PetscInt *isort)
{
  PetscErrorCode ierr;
  PetscInt       istep;       /* Chunk-sizes of already sorted parts of arrays */
  PetscInt       i, i1, i2;   /* Loop counters for (partly) sorted arrays */
  PetscInt       istart, i1end, i2end; /* start of newly sorted array part, end of both  parts */
  PetscInt       *ialloc;     /* Allocated arrays */
  PetscInt       *iswap;      /* auxiliary pointers for swapping */
  PetscInt       *ihlp1;      /* Pointers to new version of arrays, */
  PetscInt       *ihlp2;      /* Pointers to previous version of arrays, */

  PetscFunctionBegin;
  ierr = PetscMalloc(nrows*sizeof(PetscInt),&ialloc);CHKERRQ(ierr);

  ihlp1 = ialloc;
  ihlp2 = isort;

  /* Sorted array chunks are first 1 long, and increase until they are the complete array */
  for (istep=1; istep<nrows; istep*=2) {
    /*
      Combine sorted parts
          istart:istart+istep-1 and istart+istep-1:istart+2*istep-1
      of ihlp2 and vhlp2

      into one sorted part
          istart:istart+2*istep-1
      of ihlp1 and vhlp1
    */
    for (istart=0; istart<nrows; istart+=2*istep) {
      /* Set counters and bound array part endings */
      i1=istart;        i1end = i1+istep;  if (i1end>nrows) {i1end=nrows;}
      i2=istart+istep;  i2end = i2+istep;  if (i2end>nrows) {i2end=nrows;}

      /* Merge the two array parts */
      for (i=istart; i<i2end; i++)  {
        if (i1<i1end && i2<i2end && spbas_row_order_icol(ihlp2[i1], ihlp2[i2], irow_in, icol_in, col_idx_type) < 0) {
          ihlp1[i] = ihlp2[i1];
          i1++;
        } else if (i2<i2end) {
          ihlp1[i] = ihlp2[i2];
          i2++;
        } else {
          ihlp1[i] = ihlp2[i1];
          i1++;
        }
      }
    }

    /* Swap the two array sets */
    iswap = ihlp2; ihlp2 = ihlp1; ihlp1 = iswap;
  }

  /* Copy one more time in case the sorted arrays are the temporary ones */
  if (ihlp2 != isort) {
    for (i=0; i<nrows; i++) { isort[i] = ihlp2[i]; }
  }
  ierr = PetscFree(ialloc);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}



/*
  spbas_compress_pattern:
     calculate a compressed sparseness pattern for a sparseness pattern
     given in compressed row storage. The compressed sparseness pattern may
     require (much) less memory.
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_compress_pattern"
PetscErrorCode spbas_compress_pattern(PetscInt *irow_in, PetscInt *icol_in, PetscInt nrows, PetscInt ncols, PetscInt col_idx_type, spbas_matrix *B,PetscReal *mem_reduction)
{
  PetscInt         nnz = irow_in[nrows];
  long int         mem_orig = (nrows + nnz) * sizeof(PetscInt);
  long int         mem_compressed;
  PetscErrorCode   ierr;
  PetscInt         *isort;
  PetscInt         *icols;
  PetscInt         row_nnz;
  PetscInt         *ipoint;
  PetscBool        *used;
  PetscInt         ptr;
  PetscInt         i,j;
  const PetscBool  no_values = PETSC_FALSE;

  PetscFunctionBegin;
  /* Allocate the structure of the new matrix */
  B->nrows = nrows;
  B->ncols = ncols;
  B->nnz   = nnz;
  B->col_idx_type= col_idx_type;
  B->block_data = PETSC_TRUE;
  ierr = spbas_allocate_pattern(B, no_values);CHKERRQ(ierr);

  /* When using an offset array, set it */
  if (col_idx_type==SPBAS_OFFSET_ARRAY)  {
    for (i=0; i<nrows; i++) {B->icol0[i] = icol_in[irow_in[i]];}
  }

  /* Allocate the ordering for the rows */
  ierr = PetscMalloc(nrows*sizeof(PetscInt),&isort);CHKERRQ(ierr);
  ierr = PetscMalloc(nrows*sizeof(PetscInt),&ipoint);CHKERRQ(ierr);
  ierr = PetscMalloc(nrows*sizeof(PetscBool),&used);CHKERRQ(ierr);

  /*  Initialize the sorting */
  ierr = PetscMemzero((void*) used, nrows*sizeof(PetscBool));CHKERRQ(ierr);
  for (i = 0; i<nrows; i++)  {
    B->row_nnz[i] = irow_in[i+1]-irow_in[i];
    isort[i] = i;
    ipoint[i]= i;
  }

  /* Sort the rows so that identical columns will be next to each other */
  ierr = spbas_mergesort_icols(nrows, irow_in, icol_in, col_idx_type, isort);CHKERRQ(ierr);
  ierr = PetscInfo(PETSC_NULL,"Rows have been sorted for patterns\n");CHKERRQ(ierr);

  /* Replace identical rows with the first one in the list */
  for (i=1; i<nrows; i++) {
    if (spbas_row_order_icol(isort[i-1], isort[i], irow_in, icol_in, col_idx_type) == 0) {
      ipoint[isort[i]] = ipoint[isort[i-1]];
    }
  }

  /* Collect the rows which are used*/
  for (i=0; i<nrows; i++) {used[ipoint[i]] = PETSC_TRUE;}

  /* Calculate needed memory */
  B->n_alloc_icol = 0;
  for (i=0; i<nrows; i++)  {
    if (used[i]) {B->n_alloc_icol += B->row_nnz[i];}
  }
  ierr = PetscMalloc(B->n_alloc_icol*sizeof(PetscInt),&B->alloc_icol);CHKERRQ(ierr);

  /* Fill in the diagonal offsets for the rows which store their own data */
  ptr = 0;
  for (i=0; i<B->nrows; i++) {
    if (used[i])  {
      B->icols[i] = &B->alloc_icol[ptr];
      icols = &icol_in[irow_in[i]];
      row_nnz = B->row_nnz[i];
      if (col_idx_type == SPBAS_COLUMN_NUMBERS) {
        for (j=0; j<row_nnz; j++) {
          B->icols[i][j] = icols[j];
        }
      } else if (col_idx_type == SPBAS_DIAGONAL_OFFSETS) {
        for (j=0; j<row_nnz; j++) {
          B->icols[i][j] = icols[j]-i;
        }
      } else if (col_idx_type == SPBAS_OFFSET_ARRAY) {
        for (j=0; j<row_nnz; j++) {
          B->icols[i][j] = icols[j]-icols[0];
        }
      }
      ptr += B->row_nnz[i];
    }
  }

  /* Point to the right places for all data */
  for (i=0; i<nrows; i++) {
    B->icols[i] = B->icols[ipoint[i]];
  }
  ierr = PetscInfo(PETSC_NULL,"Row patterns have been compressed\n");CHKERRQ(ierr);
  ierr = PetscInfo1(PETSC_NULL,"         (%G nonzeros per row)\n",  (PetscReal) nnz / (PetscReal) nrows);CHKERRQ(ierr);

  ierr=PetscFree(isort);CHKERRQ(ierr);
  ierr=PetscFree(used);CHKERRQ(ierr);
  ierr=PetscFree(ipoint);CHKERRQ(ierr);

  mem_compressed = spbas_memory_requirement(*B);
  *mem_reduction = 100.0 * (PetscReal)(mem_orig-mem_compressed)/ (PetscReal) mem_orig;
  PetscFunctionReturn(0);
}

/*
   spbas_incomplete_cholesky
       Incomplete Cholesky decomposition
*/
#include <../src/mat/impls/aij/seq/bas/spbas_cholesky.h>

/*
  spbas_delete : de-allocate the arrays owned by this matrix
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_delete"
PetscErrorCode spbas_delete(spbas_matrix matrix)
{
  PetscInt       i;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  if (matrix.block_data) {
    ierr=PetscFree(matrix.alloc_icol);CHKERRQ(ierr);
    if (matrix.values) {ierr=PetscFree(matrix.alloc_val);CHKERRQ(ierr);}
  } else  {
    for (i=0; i<matrix.nrows; i++) { ierr=PetscFree(matrix.icols[i]);CHKERRQ(ierr);}
    ierr = PetscFree(matrix.icols);CHKERRQ(ierr);
    if (matrix.values) {
      for (i=0; i<matrix.nrows; i++) { ierr=PetscFree(matrix.values[i]);CHKERRQ(ierr);}
    }
  }

  ierr=PetscFree(matrix.row_nnz);CHKERRQ(ierr);
  ierr=PetscFree(matrix.icols);CHKERRQ(ierr);
  if (matrix.col_idx_type == SPBAS_OFFSET_ARRAY) {ierr=PetscFree(matrix.icol0);CHKERRQ(ierr);}
  ierr=PetscFree(matrix.values);CHKERRQ(ierr);
   PetscFunctionReturn(0);
}

/*
spbas_matrix_to_crs:
   Convert an spbas_matrix to compessed row storage
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_matrix_to_crs"
PetscErrorCode spbas_matrix_to_crs(spbas_matrix matrix_A,MatScalar **val_out, PetscInt **irow_out, PetscInt **icol_out)
{
  PetscInt       nrows = matrix_A.nrows;
  PetscInt       nnz   = matrix_A.nnz;
  PetscInt       i,j,r_nnz,i0;
  PetscInt       *irow;
  PetscInt       *icol;
  PetscInt       *icol_A;
  MatScalar      *val;
  PetscScalar    *val_A;
  PetscInt       col_idx_type = matrix_A.col_idx_type;
  PetscBool      do_values = matrix_A.values ? PETSC_TRUE : PETSC_FALSE;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = PetscMalloc(sizeof(PetscInt) * (nrows+1), &irow);CHKERRQ(ierr);
  ierr = PetscMalloc(sizeof(PetscInt) * nnz, &icol);CHKERRQ(ierr);
  *icol_out = icol;
  *irow_out=irow;
  if (do_values)  {
  ierr = PetscMalloc(sizeof(MatScalar) * nnz, &val);CHKERRQ(ierr);
  *val_out = val; *icol_out = icol; *irow_out=irow;
  }

  irow[0]=0;
  for (i=0; i<nrows; i++) {
    r_nnz = matrix_A.row_nnz[i];
    i0 = irow[i];
    irow[i+1] = i0 + r_nnz;
    icol_A = matrix_A.icols[i];

    if (do_values) {
      val_A = matrix_A.values[i];
      for (j=0; j<r_nnz; j++) {
          icol[i0+j] = icol_A[j];
          val[i0+j]  = val_A[j];
      }
    } else {
      for (j=0; j<r_nnz; j++) { icol[i0+j] = icol_A[j]; }
    }

    if (col_idx_type == SPBAS_DIAGONAL_OFFSETS) {
      for (j=0; j<r_nnz; j++) { icol[i0+j] += i; }
    }
    else if (col_idx_type == SPBAS_OFFSET_ARRAY) {
      i0 = matrix_A.icol0[i];
      for (j=0; j<r_nnz; j++) { icol[i0+j] += i0; }
    }
  }
  PetscFunctionReturn(0);
}


/*
    spbas_transpose
       return the transpose of a matrix
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_transpose"
PetscErrorCode spbas_transpose(spbas_matrix in_matrix, spbas_matrix * result)
{
  PetscInt       col_idx_type = in_matrix.col_idx_type;
  PetscInt       nnz   = in_matrix.nnz;
  PetscInt       ncols = in_matrix.nrows;
  PetscInt       nrows = in_matrix.ncols;
  PetscInt       i,j,k;
  PetscInt       r_nnz;
  PetscInt       *irow;
  PetscInt       icol0 = 0;
  PetscScalar    * val;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  /* Copy input values */
  result->nrows        = nrows;
  result->ncols        = ncols;
  result->nnz          = nnz;
  result->col_idx_type = SPBAS_COLUMN_NUMBERS;
  result->block_data   = PETSC_TRUE;

  /* Allocate sparseness pattern */
  ierr =  spbas_allocate_pattern(result, in_matrix.values ? PETSC_TRUE : PETSC_FALSE);CHKERRQ(ierr);

  /*  Count the number of nonzeros in each row */
  for (i = 0; i<nrows; i++) { result->row_nnz[i] = 0; }

  for (i=0; i<ncols; i++) {
    r_nnz = in_matrix.row_nnz[i];
    irow  = in_matrix.icols[i];
    if (col_idx_type == SPBAS_COLUMN_NUMBERS)  {
      for (j=0; j<r_nnz; j++) { result->row_nnz[irow[j]]++; }
    } else if (col_idx_type == SPBAS_DIAGONAL_OFFSETS)  {
      for (j=0; j<r_nnz; j++) { result->row_nnz[i+irow[j]]++; }
    } else if (col_idx_type == SPBAS_OFFSET_ARRAY) {
      icol0=in_matrix.icol0[i];
      for (j=0; j<r_nnz; j++) { result->row_nnz[icol0+irow[j]]++; }
    }
  }

  /* Set the pointers to the data */
  ierr = spbas_allocate_data(result);CHKERRQ(ierr);

  /* Reset the number of nonzeros in each row */
  for (i = 0; i<nrows; i++) { result->row_nnz[i] = 0; }

  /* Fill the data arrays */
  if (in_matrix.values) {
    for (i=0; i<ncols; i++) {
      r_nnz = in_matrix.row_nnz[i];
      irow  = in_matrix.icols[i];
      val   = in_matrix.values[i];

      if      (col_idx_type == SPBAS_COLUMN_NUMBERS)   {icol0=0;}
      else if (col_idx_type == SPBAS_DIAGONAL_OFFSETS) {icol0=i;}
      else if (col_idx_type == SPBAS_OFFSET_ARRAY)     {icol0=in_matrix.icol0[i];}
      for (j=0; j<r_nnz; j++)  {
        k = icol0 + irow[j];
        result->icols[k][result->row_nnz[k]]  = i;
        result->values[k][result->row_nnz[k]] = val[j];
        result->row_nnz[k]++;
      }
    }
  }  else {
    for (i=0; i<ncols; i++) {
      r_nnz = in_matrix.row_nnz[i];
      irow  = in_matrix.icols[i];

      if      (col_idx_type == SPBAS_COLUMN_NUMBERS)   {icol0=0;}
      else if (col_idx_type == SPBAS_DIAGONAL_OFFSETS) {icol0=i;}
      else if (col_idx_type == SPBAS_OFFSET_ARRAY)     {icol0=in_matrix.icol0[i];}

      for (j=0; j<r_nnz; j++) {
        k = icol0 + irow[j];
        result->icols[k][result->row_nnz[k]]  = i;
        result->row_nnz[k]++;
      }
    }
  }
  PetscFunctionReturn(0);
}

/*
   spbas_mergesort

      mergesort for an array of intergers and an array of associated
      reals

      on output, icol[0..nnz-1] is increasing;
                  val[0..nnz-1] has undergone the same permutation as icol

      NB: val may be PETSC_NULL: in that case, only the integers are sorted

*/
#undef __FUNCT__
#define __FUNCT__ "spbas_mergesort"
PetscErrorCode spbas_mergesort(PetscInt nnz, PetscInt *icol, PetscScalar *val)
{
  PetscInt       istep;       /* Chunk-sizes of already sorted parts of arrays */
  PetscInt       i, i1, i2;   /* Loop counters for (partly) sorted arrays */
  PetscInt       istart, i1end, i2end; /* start of newly sorted array part, end of both parts */
  PetscInt       *ialloc;     /* Allocated arrays */
  PetscScalar    *valloc=PETSC_NULL;
  PetscInt       *iswap;      /* auxiliary pointers for swapping */
  PetscScalar    *vswap;
  PetscInt       *ihlp1;      /* Pointers to new version of arrays, */
  PetscScalar    *vhlp1=PETSC_NULL;  /* (arrays under construction) */
  PetscInt       *ihlp2;      /* Pointers to previous version of arrays, */
  PetscScalar    *vhlp2=PETSC_NULL;
  PetscErrorCode ierr;

  ierr = PetscMalloc(nnz*sizeof(PetscInt),&ialloc);CHKERRQ(ierr);
  ihlp1 = ialloc;
  ihlp2 = icol;

  if (val) {
    ierr = PetscMalloc(nnz*sizeof(PetscScalar),&valloc);CHKERRQ(ierr);
    vhlp1 = valloc;
    vhlp2 = val;
  }


  /* Sorted array chunks are first 1 long, and increase until they are the complete array */
  for (istep=1; istep<nnz; istep*=2) {
    /*
      Combine sorted parts
          istart:istart+istep-1 and istart+istep-1:istart+2*istep-1
      of ihlp2 and vhlp2

      into one sorted part
          istart:istart+2*istep-1
      of ihlp1 and vhlp1
    */
    for (istart=0; istart<nnz; istart+=2*istep) {
      /* Set counters and bound array part endings */
      i1=istart;        i1end = i1+istep;  if (i1end>nnz) {i1end=nnz;}
      i2=istart+istep;  i2end = i2+istep;  if (i2end>nnz) {i2end=nnz;}

      /* Merge the two array parts */
      if (val) {
        for (i=istart; i<i2end; i++) {
          if (i1<i1end && i2<i2end && ihlp2[i1] < ihlp2[i2]) {
              ihlp1[i] = ihlp2[i1];
              vhlp1[i] = vhlp2[i1];
              i1++;
          } else if (i2<i2end) {
              ihlp1[i] = ihlp2[i2];
              vhlp1[i] = vhlp2[i2];
              i2++;
          } else {
              ihlp1[i] = ihlp2[i1];
              vhlp1[i] = vhlp2[i1];
              i1++;
          }
        }
      } else {
        for (i=istart; i<i2end; i++) {
          if (i1<i1end && i2<i2end && ihlp2[i1] < ihlp2[i2]) {
              ihlp1[i] = ihlp2[i1];
              i1++;
          } else if (i2<i2end) {
              ihlp1[i] = ihlp2[i2];
              i2++;
          } else {
              ihlp1[i] = ihlp2[i1];
              i1++;
          }
        }
      }
    }

    /* Swap the two array sets */
    iswap = ihlp2; ihlp2 = ihlp1; ihlp1 = iswap;
    vswap = vhlp2; vhlp2 = vhlp1; vhlp1 = vswap;
  }

  /* Copy one more time in case the sorted arrays are the temporary ones */
  if (ihlp2 != icol) {
    for (i=0; i<nnz; i++) { icol[i] = ihlp2[i]; }
    if (val) {
      for (i=0; i<nnz; i++) { val[i] = vhlp2[i]; }
    }
  }

  ierr = PetscFree(ialloc);CHKERRQ(ierr);
  if (val) {ierr = PetscFree(valloc);CHKERRQ(ierr);}
  PetscFunctionReturn(0);
}

/*
  spbas_apply_reordering_rows:
    apply the given reordering to the rows:  matrix_A = matrix_A(perm,:);
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_apply_reordering_rows"
PetscErrorCode spbas_apply_reordering_rows(spbas_matrix *matrix_A, const PetscInt *permutation)
{
  PetscInt       i,j,ip;
  PetscInt       nrows=matrix_A->nrows;
  PetscInt       * row_nnz;
  PetscInt       **icols;
  PetscBool      do_values = matrix_A->values ? PETSC_TRUE : PETSC_FALSE;
  PetscScalar    **vals=PETSC_NULL;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  if (matrix_A->col_idx_type != SPBAS_DIAGONAL_OFFSETS) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP_SYS,"must have diagonal offsets in pattern\n");

  if (do_values)  {
    ierr = PetscMalloc(sizeof(PetscScalar*)*nrows, &vals);CHKERRQ(ierr);
  }
  ierr = PetscMalloc(sizeof(PetscInt)*nrows, &row_nnz);CHKERRQ(ierr);
  ierr = PetscMalloc(sizeof(PetscInt*)*nrows, &icols);CHKERRQ(ierr);

  for (i=0; i<nrows;i++) {
    ip = permutation[i];
    if (do_values) {vals[i]    = matrix_A->values[ip];}
    icols[i]   = matrix_A->icols[ip];
    row_nnz[i] = matrix_A->row_nnz[ip];
    for (j=0; j<row_nnz[i]; j++) { icols[i][j] += ip-i; }
  }

  if (do_values) { ierr = PetscFree(matrix_A->values);CHKERRQ(ierr);}
  ierr = PetscFree(matrix_A->icols);CHKERRQ(ierr);
  ierr = PetscFree(matrix_A->row_nnz);CHKERRQ(ierr);

  if (do_values) { matrix_A->values  = vals; }
  matrix_A->icols   = icols;
  matrix_A->row_nnz = row_nnz;

  PetscFunctionReturn(0);
}


/*
  spbas_apply_reordering_cols:
    apply the given reordering to the columns:  matrix_A(:,perm) = matrix_A;
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_apply_reordering_cols"
PetscErrorCode spbas_apply_reordering_cols(spbas_matrix *matrix_A,const PetscInt *permutation)
{
  PetscInt    i,j;
  PetscInt    nrows=matrix_A->nrows;
  PetscInt    row_nnz;
  PetscInt    *icols;
  PetscBool   do_values = matrix_A->values ? PETSC_TRUE : PETSC_FALSE;
  PetscScalar *vals=PETSC_NULL;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  if (matrix_A->col_idx_type != SPBAS_DIAGONAL_OFFSETS) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP_SYS, "must have diagonal offsets in pattern\n");

  for (i=0; i<nrows;i++) {
    icols   = matrix_A->icols[i];
    row_nnz = matrix_A->row_nnz[i];
    if (do_values) { vals = matrix_A->values[i]; }

    for (j=0; j<row_nnz; j++)  {
        icols[j] = permutation[i+icols[j]]-i;
    }
    ierr = spbas_mergesort(row_nnz, icols, vals);CHKERRQ(ierr);
  }
  PetscFunctionReturn(0);
}

/*
  spbas_apply_reordering:
    apply the given reordering:  matrix_A(perm,perm) = matrix_A;
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_apply_reordering"
PetscErrorCode spbas_apply_reordering(spbas_matrix *matrix_A, const PetscInt *permutation, const PetscInt * inv_perm)
{
  PetscErrorCode ierr;

  PetscFunctionBegin;
  ierr = spbas_apply_reordering_rows(matrix_A, inv_perm);CHKERRQ(ierr);
  ierr = spbas_apply_reordering_cols(matrix_A, permutation);CHKERRQ(ierr);
  PetscFunctionReturn(0);
}

#undef __FUNCT__
#define __FUNCT__ "spbas_pattern_only"
PetscErrorCode spbas_pattern_only(PetscInt nrows, PetscInt ncols, PetscInt *ai, PetscInt *aj, spbas_matrix * result)
{
  spbas_matrix   retval;
  PetscInt       i, j, i0, r_nnz;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  /* Copy input values */
  retval.nrows = nrows;
  retval.ncols = ncols;
  retval.nnz   = ai[nrows];

  retval.block_data   = PETSC_TRUE;
  retval.col_idx_type = SPBAS_DIAGONAL_OFFSETS;

  /* Allocate output matrix */
  ierr =  spbas_allocate_pattern(&retval, PETSC_FALSE);CHKERRQ(ierr);
  for (i=0; i<nrows; i++)  {retval.row_nnz[i] = ai[i+1]-ai[i];}
  ierr =  spbas_allocate_data(&retval);CHKERRQ(ierr);
  /* Copy the structure */
  for (i = 0; i<retval.nrows; i++)  {
    i0 = ai[i];
    r_nnz = ai[i+1]-i0;

    for (j=0; j<r_nnz; j++) {
      retval.icols[i][j]  = aj[i0+j]-i;
    }
  }
  *result = retval;
  PetscFunctionReturn(0);
}


/*
   spbas_mark_row_power:
      Mark the columns in row 'row' which are nonzero in
          matrix^2log(marker).
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_mark_row_power"
PetscErrorCode spbas_mark_row_power(PetscInt *iwork,             /* marker-vector */
                                    PetscInt row,                /* row for which the columns are marked */
                                    spbas_matrix * in_matrix,    /* matrix for which the power is being  calculated */
                                    PetscInt marker,             /* marker-value: 2^power */
                                    PetscInt minmrk,             /* lower bound for marked points */
                                    PetscInt maxmrk)             /* upper bound for marked points */
{
  PetscErrorCode ierr;
  PetscInt       i,j, nnz;

  PetscFunctionBegin;
  nnz = in_matrix->row_nnz[row];

  /* For higher powers, call this function recursively */
  if (marker>1) {
    for (i=0; i<nnz;i++) {
      j = row + in_matrix->icols[row][i];
      if (minmrk<=j && j<maxmrk && iwork[j] < marker) {
        ierr =  spbas_mark_row_power(iwork, row + in_matrix->icols[row][i],in_matrix, marker/2,minmrk,maxmrk);CHKERRQ(ierr);
        iwork[j] |= marker;
      }
    }
  } else  {
    /*  Mark the columns reached */
    for (i=0; i<nnz;i++)  {
      j = row + in_matrix->icols[row][i];
      if (minmrk<=j && j<maxmrk) { iwork[j] |= 1; }
    }
  }
  PetscFunctionReturn(0);
}


/*
   spbas_power
      Calculate sparseness patterns for incomplete Cholesky decompositions
      of a given order: (almost) all nonzeros of the matrix^(order+1) which
      are inside the band width are found and stored in the output sparseness
      pattern.
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_power"
PetscErrorCode spbas_power (spbas_matrix in_matrix,PetscInt power, spbas_matrix * result)
{
  spbas_matrix   retval;
  PetscInt       nrows = in_matrix.nrows;
  PetscInt       ncols = in_matrix.ncols;
  PetscInt       i, j, kend;
  PetscInt       nnz, inz;
  PetscInt       *iwork;
  PetscInt       marker;
  PetscInt       maxmrk=0;
  PetscErrorCode ierr;

  PetscFunctionBegin;
  if (in_matrix.col_idx_type != SPBAS_DIAGONAL_OFFSETS) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP_SYS,"must have diagonal offsets in pattern\n");
  if (ncols != nrows) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Dimension error\n");
  if (in_matrix.values) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_ARG_INCOMP, "Input array must be sparseness pattern (no values)");
  if (power<=0) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP_SYS, "Power must be 1 or up");

  /* Copy input values*/
  retval.nrows = ncols;
  retval.ncols = nrows;
  retval.nnz   = 0;
  retval.col_idx_type = SPBAS_DIAGONAL_OFFSETS;
  retval.block_data = PETSC_FALSE;

  /* Allocate sparseness pattern */
  ierr =  spbas_allocate_pattern(&retval, in_matrix.values ? PETSC_TRUE : PETSC_FALSE);CHKERRQ(ierr);

  /* Allocate marker array */
  ierr = PetscMalloc(nrows * sizeof(PetscInt), &iwork);CHKERRQ(ierr);

  /* Erase the pattern for this row */
  ierr = PetscMemzero((void *) iwork, retval.nrows*sizeof(PetscInt));CHKERRQ(ierr);

  /* Calculate marker values */
  marker = 1; for (i=1; i<power; i++) {marker*=2;}

  for (i=0; i<nrows; i++)  {
    /* Calculate the pattern for each row */

    nnz    = in_matrix.row_nnz[i];
    kend   = i+in_matrix.icols[i][nnz-1];
    if (maxmrk<=kend) {maxmrk=kend+1;}
    ierr =  spbas_mark_row_power(iwork, i, &in_matrix, marker, i, maxmrk);CHKERRQ(ierr);

    /* Count the columns*/
    nnz = 0;
    for (j=i; j<maxmrk; j++) {nnz+= (iwork[j]!=0);}

    /* Allocate the column indices */
    retval.row_nnz[i] = nnz;
    ierr = PetscMalloc(nnz*sizeof(PetscInt),&retval.icols[i]);CHKERRQ(ierr);

    /* Administrate the column indices */
    inz = 0;
    for (j=i; j<maxmrk; j++) {
      if (iwork[j])  {
        retval.icols[i][inz] = j-i;
        inz++;
        iwork[j]=0;
      }
    }
    retval.nnz += nnz;
  };
  ierr = PetscFree(iwork);CHKERRQ(ierr);
  *result = retval;
  PetscFunctionReturn(0);
}



/*
   spbas_keep_upper:
      remove the lower part of the matrix: keep the upper part
*/
#undef __FUNCT__
#define __FUNCT__ "spbas_keep_upper"
PetscErrorCode spbas_keep_upper(spbas_matrix * inout_matrix)
{
  PetscInt i, j;
  PetscInt jstart;

  PetscFunctionBegin;
  if (inout_matrix->block_data) SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP_SYS, "Not yet for block data matrices\n");
  for (i=0; i<inout_matrix->nrows; i++)  {
    for (jstart=0; (jstart<inout_matrix->row_nnz[i]) && (inout_matrix->icols[i][jstart]<0); jstart++) {}
    if (jstart>0) {
      for (j=0; j<inout_matrix->row_nnz[i]-jstart; j++) {
        inout_matrix->icols[i][j] =  inout_matrix->icols[i][j+jstart];
      }

      if (inout_matrix->values) {
        for (j=0; j<inout_matrix->row_nnz[i]-jstart; j++) {
          inout_matrix->values[i][j] = inout_matrix->values[i][j+jstart];
        }
      }

      inout_matrix->row_nnz[i] -= jstart;

      inout_matrix->icols[i] = (PetscInt*) realloc((void*) inout_matrix->icols[i], inout_matrix->row_nnz[i]*sizeof(PetscInt));

      if (inout_matrix->values) {
        inout_matrix->values[i] = (PetscScalar*) realloc((void*) inout_matrix->values[i], inout_matrix->row_nnz[i]*sizeof(PetscScalar));
      }
      inout_matrix->nnz -= jstart;
    }
  }
  PetscFunctionReturn(0);
}