Date: 2013-07-02T14:42:34+00:00

Actual source code: dgefa.c
petsc-3.4.2 2013-07-02

      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>

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

     24: /*     gaussian elimination with partial pivoting */

     27:   /* Parameter adjustments */
     28:   --ipvt;
     29:   a -= n + 1;

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

     38: /*        find l = pivot index */

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

     51:     if (a[l + kn] == 0.0) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_LU_ZRPVT,"Zero pivot, row %D",k-1);

     53: /*           interchange if necessary */

     55:     if (l != k) {
     56:       t         = a[l + kn];
     57:       a[l + kn] = a[knp1];
     58:       a[knp1]   = t;
     59:     }

     61: /*           compute multipliers */

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

     68: /*           row elimination with column indexing */

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

     79:       i__3 = n - k;
     80:       ay   = &a[1+k+jn1];
     81:       for (ll=0; ll<i__3; ll++) ay[ll] += t*ax[ll];
     82:     }
     83:   }
     84:   ipvt[n] = n;
     85:   if (a[n + n * n] == 0.0) SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_LU_ZRPVT,"Zero pivot, row %D",n-1);
     86:   return(0);
     87: }