Date: 2022-03-04T17:37:48+00:00

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;

     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) { max = tmp; l = ll+1;}
     45:     }
     46:     l      += k - 1;
     47:     ipvt[k] = l;

     49:     if (a[l + kn] == 0.0) {
     50:       if (allowzeropivot) {
     52:         PetscInfo1(NULL,"Zero pivot, row %D\n",k-1);
     53:         if (zeropivotdetected) *zeropivotdetected = PETSC_TRUE;
     54:       } else SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_LU_ZRPVT,"Zero pivot, row %D",k-1);
     55:     }

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

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

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

     80:       i__3 = n - k;
     81:       ay   = &a[1+k+jn1];
     82:       for (ll=0; ll<i__3; ll++) ay[ll] += t*ax[ll];
     83:     }
     84:   }
     85:   ipvt[n] = n;
     86:   if (a[n + n * n] == 0.0) {
     87:     if (allowzeropivot) {
     89:       PetscInfo1(NULL,"Zero pivot, row %D\n",n-1);
     90:       if (zeropivotdetected) *zeropivotdetected = PETSC_TRUE;
     91:     } else SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_LU_ZRPVT,"Zero pivot, row %D",n-1);
     92:   }
     93:   return(0);
     94: }