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: */
 35: PetscErrorCode  MatReorderingSeqSBAIJ(Mat A,IS perm)
 36: {
 37:   Mat_SeqSBAIJ   *a=(Mat_SeqSBAIJ*)A->data;
 38:   const PetscInt mbs=a->mbs;

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

 51:   ISInvertPermutation(perm,PETSC_DECIDE,&iperm);
 52:   ISGetIndices(iperm,&riip);

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

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

 68:   /*
 69:      Phase 1: Find row index r in which to store each nonzero.
 70:               Initialize count of nonzeros to be stored in each row (nzr).
 71:               At the end of this phase, a nonzero a(*,*)=a(r(),aj())
 72:               s.t. a(perm(r),perm(aj)) will fall into upper triangle part.
 73:   */

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

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

 93:       r[j] = k; j++;
 94:       nzr[k]++;  /* increment count of nonzeros in that row */
 95:     }
 96:   }

 98:   /* Phase 2: Find new ai and permutation to apply to (aj,a).
 99:               Determine pointers (r) to delimit rows in permuted (aj,a).
100:               Note: r is different from r used in phase 1.
101:               At the end of this phase, (aj[j],a[j]) will be stored in
102:               (aj[r(j)],a[r(j)]).
103:   */
104:   for (i=0; i<mbs; i++) {
105:     ai[i+1] = ai[i] + nzr[i];
106:     nzr[i]  = ai[i+1];
107:   }

109:   /* determine where each (aj[j], a[j]) is stored in new (aj,a)
110:      for each nonzero element (in reverse order) */
111:   jmin = ai[0]; jmax = ai[mbs];
112:   nz   = jmax - jmin;
113:   j    = jmax-1;
114:   while (nz--) {
115:     i = r[j];  /* row value */
116:     if (aj[j] == i) r[j] = ai[i]; /* put diagonal nonzero at beginning of row */
117:     else { /* put off-diagonal nonzero in last unused location in row */
118:       nzr[i]--; r[j] = nzr[i];
119:     }
120:     j--;
121:   }

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

126:   /* Phase 3: permute (aj,a) to upper triangular form (wrt new ordering) */
127:   for (j=jmin; j<jmax; j++) {
128:     while (r[j] != j) {
129:       k   = r[j]; r[j] = r[k]; r[k] = k;
130:       ajk = aj[k]; aj[k] = aj[j]; aj[j] = ajk;
131:       /* ak = aa[k]; aa[k] = aa[j]; aa[j] = ak; */
132:     }
133:   }
134:   ierr= ISRestoreIndices(perm,&rip);

136:   a->inew = ai;
137:   a->jnew = aj;

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

148:   PetscFree(nzr);
149:   PetscFree(r);
150:   return(0);
151: #endif
152: }