xref: /petsc/src/mat/impls/sbaij/seq/sro.c (revision d71ae5a4db6382e7f06317b8d368875286fe9008)

#include <../src/mat/impls/baij/seq/baij.h>
#include <../src/mat/impls/sbaij/seq/sbaij.h>

/*
This function is used before applying a
symmetric reordering to matrix A that is
in SBAIJ format.

The permutation is assumed to be symmetric, i.e.,
P = P^T (= inv(P)),
so the permuted matrix P*A*inv(P)=P*A*P^T is ensured to be symmetric.
 - a wrong assumption! This code needs rework!  -- Hong

The function is modified from sro.f of YSMP. The description from YSMP:
C    THE NONZERO ENTRIES OF THE MATRIX M ARE ASSUMED TO BE STORED
C    SYMMETRICALLY IN (IA,JA,A) FORMAT (I.E., NOT BOTH M(I,J) AND M(J,I)
C    ARE STORED IF I NE J).
C
C    SRO DOES NOT REARRANGE THE ORDER OF THE ROWS, BUT DOES MOVE
C    NONZEROES FROM ONE ROW TO ANOTHER TO ENSURE THAT IF M(I,J) WILL BE
C    IN THE UPPER TRIANGLE OF M WITH RESPECT TO THE NEW ORDERING, THEN
C    M(I,J) IS STORED IN ROW I (AND THUS M(J,I) IS NOT STORED);  WHEREAS
C    IF M(I,J) WILL BE IN THE STRICT LOWER TRIANGLE OF M, THEN M(J,I) IS
C    STORED IN ROW J (AND THUS M(I,J) IS NOT STORED).

  -- output: new index set (inew, jnew) for A and a map a2anew that maps
             values a to anew, such that all
             nonzero A_(perm(i),iperm(k)) will be stored in the upper triangle.
             Note: matrix A is not permuted by this function!
*/
PetscErrorCode MatReorderingSeqSBAIJ(Mat A, IS perm)
{
  Mat_SeqSBAIJ  *a   = (Mat_SeqSBAIJ *)A->data;
  const PetscInt mbs = a->mbs;

  PetscFunctionBegin;
  if (!mbs) PetscFunctionReturn(0);
  SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SUP, "Matrix reordering is not supported for sbaij matrix. Use aij format");
#if 0
  const PetscInt *rip,*riip;
  PetscInt       *ai,*aj,*r;
  PetscInt       *nzr,nz,jmin,jmax,j,k,ajk,i;
  IS             iperm;  /* inverse of perm */
  PetscCall(ISGetIndices(perm,&rip));

  PetscCall(ISInvertPermutation(perm,PETSC_DECIDE,&iperm));
  PetscCall(ISGetIndices(iperm,&riip));

  for (i=0; i<mbs; i++) {
    PetscCheck(rip[i] == riip[i],PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Non-symmetric permutation, use symmetric permutation for symmetric matrices");
  }
  PetscCall(ISRestoreIndices(iperm,&riip));
  PetscCall(ISDestroy(&iperm));

  if (!a->inew) {
    PetscCall(PetscMalloc2(mbs+1,&ai, 2*a->i[mbs],&aj));
  } else {
    ai = a->inew; aj = a->jnew;
  }
  PetscCall(PetscArraycpy(ai,a->i,mbs+1));
  PetscCall(PetscArraycpy(aj,a->j,a->i[mbs]));

  /*
     Phase 1: Find row index r in which to store each nonzero.
              Initialize count of nonzeros to be stored in each row (nzr).
              At the end of this phase, a nonzero a(*,*)=a(r(),aj())
              s.t. a(perm(r),perm(aj)) will fall into upper triangle part.
  */

  PetscCall(PetscMalloc1(mbs,&nzr));
  PetscCall(PetscMalloc1(ai[mbs],&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];
    /* printf("nz = %d, j=%d\n",nz,j); */
    while (nz--) {
      /*  --- find row (=r[j]) and column (=aj[j]) in which to store a[j] ...*/
      k = aj[j];                          /* col. index */
      /* printf("nz = %d, k=%d\n", nz,k); */
      /* for entry that will be permuted into lower triangle, swap row and col. index */
      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).
              Note: r is different from r used in phase 1.
              At the end of this phase, (aj[j],a[j]) will be stored in
              (aj[r(j)],a[r(j)]).
  */
  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 new (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--;
  }

  a->a2anew = aj + ai[mbs];
  PetscCall(PetscArraycpy(a->a2anew,r,ai[mbs]));

  /* 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; */
    }
  }
  PetscCall(ISRestoreIndices(perm,&rip));

  a->inew = ai;
  a->jnew = aj;

  PetscCall(ISDestroy(&a->row));
  PetscCall(ISDestroy(&a->icol));
  PetscCall(PetscObjectReference((PetscObject)perm));
  PetscCall(ISDestroy(&a->row));
  a->row  = perm;
  PetscCall(PetscObjectReference((PetscObject)perm));
  PetscCall(ISDestroy(&a->icol));
  a->icol = perm;

  PetscCall(PetscFree(nzr));
  PetscCall(PetscFree(r));
  PetscFunctionReturn(0);
#endif
}