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: }