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:   PetscArraycpy(ai,a->i,mbs+1);
 64:   PetscArraycpy(aj,a->j,a->i[mbs]);

 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:   PetscArraycpy(a->a2anew,r,ai[mbs]);

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: }