xref: /petsc/src/mat/impls/sbaij/seq/sro.c (revision db4fd139fb79ff8a7651981cdeaefb7e43c6030b)

#include "petscsys.h"
#include "src/mat/impls/baij/seq/baij.h"
#include "src/vec/vecimpl.h"
#include "src/inline/spops.h"
#include "sbaij.h"

/*
Symmetric reordering the index of sparse symmetric matrix A
so that P*A*P^T is also stored symmetrically.
The permutation needs to be symmetric, i.e., P = P^T = inv(P).
  -- modified from sor.f of YSMP
  -- idea: reorder (ai, aj, a) (not A!) to ensure that all nonzero A_(p(i),isp(k))
           are stored in the upper triangle of P*A*P^T
*/
#undef __FUNC__
#define __FUNC__ "MatReordering_SeqSBAIJ"
int MatReordering_SeqSBAIJ(Mat A,IS isp)
{
  Mat_SeqSBAIJ     *a=(Mat_SeqSBAIJ *)A->data;
  int             *r,ierr,i,mbs=a->mbs,*ai=a->i,*aj=a->j,*rip,*riip;
  MatScalar       *aa=a->a;
  Scalar          ak;
  int             *nzr,nz,jmin,jmax,j,k,ajk;
  IS              isip;  /* inverse of isp */

  PetscFunctionBegin;
  if (!mbs) PetscFunctionReturn(0);

  ierr = ISGetIndices(isp,&rip);CHKERRQ(ierr);
  ierr = ISInvertPermutation(isp,PETSC_DECIDE,&isip);CHKERRQ(ierr);
  ierr = ISGetIndices(isip,&riip);CHKERRQ(ierr);

  for (i=0; i<mbs; i++) {
    if ( rip[i] - riip[i] != 0 ) {
      printf("Non-symm. permutation, use symm. permutation or general matrix format\n");
      break;
    }
  }

  /* Phase 1: find row in which to store each nonzero (r)
	      initialize count of nonzeros to be stored in each row (nzr) */

  nzr = (int*)PetscMalloc(mbs*sizeof(int));CHKPTRQ(nzr);
  r   = (int*)PetscMalloc(ai[mbs]*sizeof(int));CHKPTRQ(r);
  for (i=0; i<mbs; i++) nzr[i] = 0;
  for (i=0; i<ai[mbs]; i++) r[i] = 0;

  /*  for each nonzero element */
  for (i=0; i<mbs; i++){
    nz = ai[i+1] - ai[i];
    j = ai[i];
    while (nz--){
      /*  --- find row (=r[j]) and column (=aj[j]) in which to store a[j] ...*/
      k = aj[j];
      if (rip[k] < rip[i]) aj[j] = i;
      else k = i;
      r[j] = k; j++;
      nzr[k] ++; /* increment count of nonzeros in that row */
    }
  }

  /* Phase 2: find new ai and permutation to apply to (aj,a)
              determine pointers (r) to delimit rows in permuted (aj,a) */
    for (i=0; i<mbs; i++){
      ai[i+1] = ai[i] + nzr[i];
      nzr[i]    = ai[i+1];
    }

  /* determine where each (aj[j], a[j]) is stored in permuted (aj,a)
     for each nonzero element (in reverse order) */
  jmin = ai[0]; jmax = ai[mbs];
  nz = jmax - jmin;
  j = jmax-1;
  while (nz--){
    i = r[j];  /* row value */
    if (aj[j] == i) r[j] = ai[i]; /* put diagonal nonzero at beginning of row */
    else { /* put off-diagonal nonzero in last unused location in row */
      nzr[i]--; r[j] = nzr[i];
    }
    j--;
  }

  /* Phase 3: permute (aj,a) to upper triangular form (wrt new ordering) */
  for (j=jmin; j<jmax; j++){
    while (r[j] != j){
      k = r[j]; r[j] = r[k]; r[k] = k;
      ajk = aj[k]; aj[k] = aj[j]; aj[j] = ajk;
      ak = aa[k]; aa[k] = aa[j]; aa[j] = ak;
    }
  }

  ierr = ISRestoreIndices(isp,&rip);CHKERRQ(ierr);

  a->row  = isp;
  a->col  = isp;
  a->icol = isp;
  ierr = PetscObjectReference((PetscObject)isp); CHKERRQ(ierr);
  PetscFunctionReturn(0);
}