1: /*
  2:        This routine was converted by f2c from Linpack source
  3:              linpack. this version dated 08/14/78
  4:       cleve moler, university of new mexico, argonne national lab.

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

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

 12: */
 13: #include <petsc/private/kernels/blockinvert.h>

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

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

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

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

 35:     /* find l = pivot index */

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

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

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

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

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

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