Actual source code: dgefa.c


  2: /*
  3:        This routine was converted by f2c from Linpack source
  4:              linpack. this version dated 08/14/78
  5:       cleve moler, university of new mexico, argonne national lab.

  7:         Does an LU factorization with partial pivoting of a dense
  8:      n by n matrix.

 10:        Used by the sparse factorization routines in
 11:      src/mat/impls/baij/seq

 13: */
 14: #include <petscsys.h>

 16: PETSC_INTERN PetscErrorCode PetscLINPACKgefa(MatScalar *a, PetscInt n, PetscInt *ipvt, PetscBool allowzeropivot, PetscBool *zeropivotdetected)
 17: {
 18:   PetscInt  i__2, i__3, kp1, nm1, j, k, l, ll, kn, knp1, jn1;
 19:   MatScalar t, *ax, *ay, *aa;
 20:   MatReal   tmp, max;

 22:   PetscFunctionBegin;
 23:   if (zeropivotdetected) *zeropivotdetected = PETSC_FALSE;

 25:   /* Parameter adjustments */
 26:   --ipvt;
 27:   a -= n + 1;

 29:   /* Function Body */
 30:   nm1 = n - 1;
 31:   for (k = 1; k <= nm1; ++k) {
 32:     kp1  = k + 1;
 33:     kn   = k * n;
 34:     knp1 = k * n + k;

 36:     /* find l = pivot index */

 38:     i__2 = n - k + 1;
 39:     aa   = &a[knp1];
 40:     max  = PetscAbsScalar(aa[0]);
 41:     l    = 1;
 42:     for (ll = 1; ll < i__2; ll++) {
 43:       tmp = PetscAbsScalar(aa[ll]);
 44:       if (tmp > max) {
 45:         max = tmp;
 46:         l   = ll + 1;
 47:       }
 48:     }
 49:     l += k - 1;
 50:     ipvt[k] = l;

 52:     if (a[l + kn] == 0.0) {
 53:       if (allowzeropivot) {
 54:         PetscCall(PetscInfo(NULL, "Zero pivot, row %" PetscInt_FMT "\n", k - 1));
 55:         if (zeropivotdetected) *zeropivotdetected = PETSC_TRUE;
 56:       } else SETERRQ(PETSC_COMM_SELF, PETSC_ERR_MAT_LU_ZRPVT, "Zero pivot, row %" PetscInt_FMT, k - 1);
 57:     }

 59:     /* interchange if necessary */
 60:     if (l != k) {
 61:       t         = a[l + kn];
 62:       a[l + kn] = a[knp1];
 63:       a[knp1]   = t;
 64:     }

 66:     /* compute multipliers */
 67:     t    = -1. / a[knp1];
 68:     i__2 = n - k;
 69:     aa   = &a[1 + knp1];
 70:     for (ll = 0; ll < i__2; ll++) aa[ll] *= t;

 72:     /* row elimination with column indexing */
 73:     ax = aa;
 74:     for (j = kp1; j <= n; ++j) {
 75:       jn1 = j * n;
 76:       t   = a[l + jn1];
 77:       if (l != k) {
 78:         a[l + jn1] = a[k + jn1];
 79:         a[k + jn1] = t;
 80:       }

 82:       i__3 = n - k;
 83:       ay   = &a[1 + k + jn1];
 84:       for (ll = 0; ll < i__3; ll++) ay[ll] += t * ax[ll];
 85:     }
 86:   }
 87:   ipvt[n] = n;
 88:   if (a[n + n * n] == 0.0) {
 89:     if (allowzeropivot) {
 90:       PetscCall(PetscInfo(NULL, "Zero pivot, row %" PetscInt_FMT "\n", n - 1));
 91:       if (zeropivotdetected) *zeropivotdetected = PETSC_TRUE;
 92:     } else SETERRQ(PETSC_COMM_SELF, PETSC_ERR_MAT_LU_ZRPVT, "Zero pivot, row %" PetscInt_FMT, n - 1);
 93:   }
 94:   PetscFunctionReturn(PETSC_SUCCESS);
 95: }