Actual source code: sro.c
petsc-3.10.5 2019-03-28
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      2:  #include <../src/mat/impls/baij/seq/baij.h>
      3:  #include <../src/mat/impls/sbaij/seq/sbaij.h>

      5: /*
      6: This function is used before applying a
      7: symmetric reordering to matrix A that is
      8: in SBAIJ format.

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

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

     28:   -- output: new index set (inew, jnew) for A and a map a2anew that maps
     29:              values a to anew, such that all
     30:              nonzero A_(perm(i),iperm(k)) will be stored in the upper triangle.
     31:              Note: matrix A is not permuted by this function!
     32: */
     33: PetscErrorCode  MatReorderingSeqSBAIJ(Mat A,IS perm)
     34: {
     35:   Mat_SeqSBAIJ   *a=(Mat_SeqSBAIJ*)A->data;
     36:   const PetscInt mbs=a->mbs;

     39:   if (!mbs) return(0);
     40:   SETERRQ(PETSC_COMM_SELF,PETSC_ERR_SUP,"Matrix reordering is not supported for sbaij matrix. Use aij format");
     41: #if 0
     43:   const PetscInt *rip,*riip;
     44:   PetscInt       *ai,*aj,*r;
     45:   PetscInt       *nzr,nz,jmin,jmax,j,k,ajk,i;
     46:   IS             iperm;  /* inverse of perm */
     47:   ISGetIndices(perm,&rip);

     49:   ISInvertPermutation(perm,PETSC_DECIDE,&iperm);
     50:   ISGetIndices(iperm,&riip);

     52:   for (i=0; i<mbs; i++) {
     53:     if (rip[i] != riip[i]) SETERRQ(PETSC_COMM_SELF,PETSC_ERR_ARG_INCOMP,"Non-symmetric permutation, use symmetric permutation for symmetric matrices");
     54:   }
     55:   ISRestoreIndices(iperm,&riip);
     56:   ISDestroy(&iperm);

     58:   if (!a->inew) {
     59:     PetscMalloc2(mbs+1,&ai, 2*a->i[mbs],&aj);
     60:   } else {
     61:     ai = a->inew; aj = a->jnew;
     62:   }
     63:   PetscMemcpy(ai,a->i,(mbs+1)*sizeof(PetscInt));
     64:   PetscMemcpy(aj,a->j,(a->i[mbs])*sizeof(PetscInt));

     66:   /*
     67:      Phase 1: Find row index r in which to store each nonzero.
     68:               Initialize count of nonzeros to be stored in each row (nzr).
     69:               At the end of this phase, a nonzero a(*,*)=a(r(),aj())
     70:               s.t. a(perm(r),perm(aj)) will fall into upper triangle part.
     71:   */

     73:   PetscMalloc1(mbs,&nzr);
     74:   PetscMalloc1(ai[mbs],&r);
     75:   for (i=0; i<mbs; i++) nzr[i] = 0;
     76:   for (i=0; i<ai[mbs]; i++) r[i] = 0;

     78:   /*  for each nonzero element */
     79:   for (i=0; i<mbs; i++) {
     80:     nz = ai[i+1] - ai[i];
     81:     j  = ai[i];
     82:     /* printf("nz = %d, j=%d\n",nz,j); */
     83:     while (nz--) {
     84:       /*  --- find row (=r[j]) and column (=aj[j]) in which to store a[j] ...*/
     85:       k = aj[j];                          /* col. index */
     86:       /* printf("nz = %d, k=%d\n", nz,k); */
     87:       /* for entry that will be permuted into lower triangle, swap row and col. index */
     88:       if (rip[k] < rip[i]) aj[j] = i;
     89:       else k = i;

     91:       r[j] = k; j++;
     92:       nzr[k]++;  /* increment count of nonzeros in that row */
     93:     }
     94:   }

     96:   /* Phase 2: Find new ai and permutation to apply to (aj,a).
     97:               Determine pointers (r) to delimit rows in permuted (aj,a).
     98:               Note: r is different from r used in phase 1.
     99:               At the end of this phase, (aj[j],a[j]) will be stored in
    100:               (aj[r(j)],a[r(j)]).
    101:   */
    102:   for (i=0; i<mbs; i++) {
    103:     ai[i+1] = ai[i] + nzr[i];
    104:     nzr[i]  = ai[i+1];
    105:   }

    107:   /* determine where each (aj[j], a[j]) is stored in new (aj,a)
    108:      for each nonzero element (in reverse order) */
    109:   jmin = ai[0]; jmax = ai[mbs];
    110:   nz   = jmax - jmin;
    111:   j    = jmax-1;
    112:   while (nz--) {
    113:     i = r[j];  /* row value */
    114:     if (aj[j] == i) r[j] = ai[i]; /* put diagonal nonzero at beginning of row */
    115:     else { /* put off-diagonal nonzero in last unused location in row */
    116:       nzr[i]--; r[j] = nzr[i];
    117:     }
    118:     j--;
    119:   }

    121:   a->a2anew = aj + ai[mbs];
    122:   PetscMemcpy(a->a2anew,r,ai[mbs]*sizeof(PetscInt));

    124:   /* Phase 3: permute (aj,a) to upper triangular form (wrt new ordering) */
    125:   for (j=jmin; j<jmax; j++) {
    126:     while (r[j] != j) {
    127:       k   = r[j]; r[j] = r[k]; r[k] = k;
    128:       ajk = aj[k]; aj[k] = aj[j]; aj[j] = ajk;
    129:       /* ak = aa[k]; aa[k] = aa[j]; aa[j] = ak; */
    130:     }
    131:   }
    132:   ierr= ISRestoreIndices(perm,&rip);

    134:   a->inew = ai;
    135:   a->jnew = aj;

    137:   ISDestroy(&a->row);
    138:   ISDestroy(&a->icol);
    139:   PetscObjectReference((PetscObject)perm);
    140:   ISDestroy(&a->row);
    141:   a->row  = perm;
    142:   PetscObjectReference((PetscObject)perm);
    143:   ISDestroy(&a->icol);
    144:   a->icol = perm;

    146:   PetscFree(nzr);
    147:   PetscFree(r);
    148:   return(0);
    149: #endif
    150: }