Date: 2026-03-01T05:24:58+00:00

Actual source code: baijsolvnat2.c

      1: #include <../src/mat/impls/baij/seq/baij.h>
      2: #include <petsc/private/kernels/blockinvert.h>

      4: #if defined(PETSC_HAVE_XMMINTRIN_H)
      5:   #include <xmmintrin.h>
      6: #endif

      8: /*
      9:       Special case where the matrix was ILU(0) factored in the natural
     10:    ordering. This eliminates the need for the column and row permutation.
     11: */
     12: PetscErrorCode MatSolve_SeqBAIJ_2_NaturalOrdering_inplace(Mat A, Vec bb, Vec xx)
     13: {
     14:   Mat_SeqBAIJ       *a = (Mat_SeqBAIJ *)A->data;
     15:   const PetscInt     n = a->mbs, *vi, *ai = a->i, *aj = a->j, *diag = a->diag;
     16:   const MatScalar   *aa = a->a, *v;
     17:   PetscScalar       *x, s1, s2, x1, x2;
     18:   const PetscScalar *b;
     19:   PetscInt           jdx, idt, idx, nz, i;

     21:   PetscFunctionBegin;
     22:   PetscCall(VecGetArrayRead(bb, &b));
     23:   PetscCall(VecGetArray(xx, &x));

     25:   /* forward solve the lower triangular */
     26:   idx  = 0;
     27:   x[0] = b[0];
     28:   x[1] = b[1];
     29:   for (i = 1; i < n; i++) {
     30:     v  = aa + 4 * ai[i];
     31:     vi = aj + ai[i];
     32:     nz = diag[i] - ai[i];
     33:     idx += 2;
     34:     s1 = b[idx];
     35:     s2 = b[1 + idx];
     36:     while (nz--) {
     37:       jdx = 2 * (*vi++);
     38:       x1  = x[jdx];
     39:       x2  = x[1 + jdx];
     40:       s1 -= v[0] * x1 + v[2] * x2;
     41:       s2 -= v[1] * x1 + v[3] * x2;
     42:       v += 4;
     43:     }
     44:     x[idx]     = s1;
     45:     x[1 + idx] = s2;
     46:   }
     47:   /* backward solve the upper triangular */
     48:   for (i = n - 1; i >= 0; i--) {
     49:     v   = aa + 4 * diag[i] + 4;
     50:     vi  = aj + diag[i] + 1;
     51:     nz  = ai[i + 1] - diag[i] - 1;
     52:     idt = 2 * i;
     53:     s1  = x[idt];
     54:     s2  = x[1 + idt];
     55:     while (nz--) {
     56:       idx = 2 * (*vi++);
     57:       x1  = x[idx];
     58:       x2  = x[1 + idx];
     59:       s1 -= v[0] * x1 + v[2] * x2;
     60:       s2 -= v[1] * x1 + v[3] * x2;
     61:       v += 4;
     62:     }
     63:     v          = aa + 4 * diag[i];
     64:     x[idt]     = v[0] * s1 + v[2] * s2;
     65:     x[1 + idt] = v[1] * s1 + v[3] * s2;
     66:   }

     68:   PetscCall(VecRestoreArrayRead(bb, &b));
     69:   PetscCall(VecRestoreArray(xx, &x));
     70:   PetscCall(PetscLogFlops(2.0 * 4 * (a->nz) - 2.0 * A->cmap->n));
     71:   PetscFunctionReturn(PETSC_SUCCESS);
     72: }

     74: PetscErrorCode MatSolve_SeqBAIJ_2_NaturalOrdering(Mat A, Vec bb, Vec xx)
     75: {
     76:   Mat_SeqBAIJ       *a = (Mat_SeqBAIJ *)A->data;
     77:   const PetscInt     n = a->mbs, *vi, *ai = a->i, *aj = a->j, *adiag = a->diag;
     78:   PetscInt           i, k, nz, idx, idt, jdx;
     79:   const MatScalar   *aa = a->a, *v;
     80:   PetscScalar       *x, s1, s2, x1, x2;
     81:   const PetscScalar *b;

     83:   PetscFunctionBegin;
     84:   PetscCall(VecGetArrayRead(bb, &b));
     85:   PetscCall(VecGetArray(xx, &x));
     86:   /* forward solve the lower triangular */
     87:   idx  = 0;
     88:   x[0] = b[idx];
     89:   x[1] = b[1 + idx];
     90:   for (i = 1; i < n; i++) {
     91:     v   = aa + 4 * ai[i];
     92:     vi  = aj + ai[i];
     93:     nz  = ai[i + 1] - ai[i];
     94:     idx = 2 * i;
     95:     s1  = b[idx];
     96:     s2  = b[1 + idx];
     97:     PetscPrefetchBlock(vi + nz, nz, 0, PETSC_PREFETCH_HINT_NTA);
     98:     PetscPrefetchBlock(v + 4 * nz, 4 * nz, 0, PETSC_PREFETCH_HINT_NTA);
     99:     for (k = 0; k < nz; k++) {
    100:       jdx = 2 * vi[k];
    101:       x1  = x[jdx];
    102:       x2  = x[1 + jdx];
    103:       s1 -= v[0] * x1 + v[2] * x2;
    104:       s2 -= v[1] * x1 + v[3] * x2;
    105:       v += 4;
    106:     }
    107:     x[idx]     = s1;
    108:     x[1 + idx] = s2;
    109:   }

    111:   /* backward solve the upper triangular */
    112:   for (i = n - 1; i >= 0; i--) {
    113:     v   = aa + 4 * (adiag[i + 1] + 1);
    114:     vi  = aj + adiag[i + 1] + 1;
    115:     nz  = adiag[i] - adiag[i + 1] - 1;
    116:     idt = 2 * i;
    117:     s1  = x[idt];
    118:     s2  = x[1 + idt];
    119:     PetscPrefetchBlock(vi + nz, nz, 0, PETSC_PREFETCH_HINT_NTA);
    120:     PetscPrefetchBlock(v + 4 * nz, 4 * nz, 0, PETSC_PREFETCH_HINT_NTA);
    121:     for (k = 0; k < nz; k++) {
    122:       idx = 2 * vi[k];
    123:       x1  = x[idx];
    124:       x2  = x[1 + idx];
    125:       s1 -= v[0] * x1 + v[2] * x2;
    126:       s2 -= v[1] * x1 + v[3] * x2;
    127:       v += 4;
    128:     }
    129:     /* x = inv_diagonal*x */
    130:     x[idt]     = v[0] * s1 + v[2] * s2;
    131:     x[1 + idt] = v[1] * s1 + v[3] * s2;
    132:   }

    134:   PetscCall(VecRestoreArrayRead(bb, &b));
    135:   PetscCall(VecRestoreArray(xx, &x));
    136:   PetscCall(PetscLogFlops(2.0 * 4 * (a->nz) - 2.0 * A->cmap->n));
    137:   PetscFunctionReturn(PETSC_SUCCESS);
    138: }

    140: PetscErrorCode MatForwardSolve_SeqBAIJ_2_NaturalOrdering(Mat A, Vec bb, Vec xx)
    141: {
    142:   Mat_SeqBAIJ       *a = (Mat_SeqBAIJ *)A->data;
    143:   const PetscInt     n = a->mbs, *vi, *ai = a->i, *aj = a->j;
    144:   PetscInt           i, k, nz, idx, jdx;
    145:   const MatScalar   *aa = a->a, *v;
    146:   PetscScalar       *x, s1, s2, x1, x2;
    147:   const PetscScalar *b;

    149:   PetscFunctionBegin;
    150:   PetscCall(VecGetArrayRead(bb, &b));
    151:   PetscCall(VecGetArray(xx, &x));
    152:   /* forward solve the lower triangular */
    153:   idx  = 0;
    154:   x[0] = b[idx];
    155:   x[1] = b[1 + idx];
    156:   for (i = 1; i < n; i++) {
    157:     v   = aa + 4 * ai[i];
    158:     vi  = aj + ai[i];
    159:     nz  = ai[i + 1] - ai[i];
    160:     idx = 2 * i;
    161:     s1  = b[idx];
    162:     s2  = b[1 + idx];
    163:     PetscPrefetchBlock(vi + nz, nz, 0, PETSC_PREFETCH_HINT_NTA);
    164:     PetscPrefetchBlock(v + 4 * nz, 4 * nz, 0, PETSC_PREFETCH_HINT_NTA);
    165:     for (k = 0; k < nz; k++) {
    166:       jdx = 2 * vi[k];
    167:       x1  = x[jdx];
    168:       x2  = x[1 + jdx];
    169:       s1 -= v[0] * x1 + v[2] * x2;
    170:       s2 -= v[1] * x1 + v[3] * x2;
    171:       v += 4;
    172:     }
    173:     x[idx]     = s1;
    174:     x[1 + idx] = s2;
    175:   }

    177:   PetscCall(VecRestoreArrayRead(bb, &b));
    178:   PetscCall(VecRestoreArray(xx, &x));
    179:   PetscCall(PetscLogFlops(4.0 * (a->nz) - A->cmap->n));
    180:   PetscFunctionReturn(PETSC_SUCCESS);
    181: }

    183: PetscErrorCode MatBackwardSolve_SeqBAIJ_2_NaturalOrdering(Mat A, Vec bb, Vec xx)
    184: {
    185:   Mat_SeqBAIJ       *a = (Mat_SeqBAIJ *)A->data;
    186:   const PetscInt     n = a->mbs, *vi, *aj = a->j, *adiag = a->diag;
    187:   PetscInt           i, k, nz, idx, idt;
    188:   const MatScalar   *aa = a->a, *v;
    189:   PetscScalar       *x, s1, s2, x1, x2;
    190:   const PetscScalar *b;

    192:   PetscFunctionBegin;
    193:   PetscCall(VecGetArrayRead(bb, &b));
    194:   PetscCall(VecGetArray(xx, &x));

    196:   /* backward solve the upper triangular */
    197:   for (i = n - 1; i >= 0; i--) {
    198:     v   = aa + 4 * (adiag[i + 1] + 1);
    199:     vi  = aj + adiag[i + 1] + 1;
    200:     nz  = adiag[i] - adiag[i + 1] - 1;
    201:     idt = 2 * i;
    202:     s1  = b[idt];
    203:     s2  = b[1 + idt];
    204:     PetscPrefetchBlock(vi + nz, nz, 0, PETSC_PREFETCH_HINT_NTA);
    205:     PetscPrefetchBlock(v + 4 * nz, 4 * nz, 0, PETSC_PREFETCH_HINT_NTA);
    206:     for (k = 0; k < nz; k++) {
    207:       idx = 2 * vi[k];
    208:       x1  = x[idx];
    209:       x2  = x[1 + idx];
    210:       s1 -= v[0] * x1 + v[2] * x2;
    211:       s2 -= v[1] * x1 + v[3] * x2;
    212:       v += 4;
    213:     }
    214:     /* x = inv_diagonal*x */
    215:     x[idt]     = v[0] * s1 + v[2] * s2;
    216:     x[1 + idt] = v[1] * s1 + v[3] * s2;
    217:   }

    219:   PetscCall(VecRestoreArrayRead(bb, &b));
    220:   PetscCall(VecRestoreArray(xx, &x));
    221:   PetscCall(PetscLogFlops(4.0 * a->nz - A->cmap->n));
    222:   PetscFunctionReturn(PETSC_SUCCESS);
    223: }