xref: /petsc/src/mat/impls/baij/seq/dgefa.c (revision 5f8bbcca2696d61632b174eeae8a5433a128d797)

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

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

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

*/
#include <petscsys.h>

#undef __FUNCT__
#define __FUNCT__ "PetscLINPACKgefa"
PetscErrorCode PetscLINPACKgefa(MatScalar *a,PetscInt n,PetscInt *ipvt,PetscBool allowzeropivot,PetscBool *zeropivotdetected)
{
  PetscInt  i__2,i__3,kp1,nm1,j,k,l,ll,kn,knp1,jn1;
  MatScalar t,*ax,*ay,*aa;
  MatReal   tmp,max;

  /* gaussian elimination with partial pivoting */

  PetscFunctionBegin;
  if (zeropivotdetected) *zeropivotdetected = PETSC_FALSE;

  /* Parameter adjustments */
  --ipvt;
  a -= n + 1;

  /* Function Body */
  nm1 = n - 1;
  for (k = 1; k <= nm1; ++k) {
    kp1  = k + 1;
    kn   = k*n;
    knp1 = k*n + k;

    /* find l = pivot index */

    i__2 = n - k + 1;
    aa   = &a[knp1];
    max  = PetscAbsScalar(aa[0]);
    l    = 1;
    for (ll=1; ll<i__2; ll++) {
      tmp = PetscAbsScalar(aa[ll]);
      if (tmp > max) { max = tmp; l = ll+1;}
    }
    l      += k - 1;
    ipvt[k] = l;

    if (a[l + kn] == 0.0) {
      if (allowzeropivot) {
        PetscErrorCode ierr;
        ierr = PetscInfo1(NULL,"Zero pivot, row %D\n",k-1);CHKERRQ(ierr);
        *zeropivotdetected = PETSC_TRUE;
      } else SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_LU_ZRPVT,"Zero pivot, row %D",k-1);
    }

    /* interchange if necessary */
    if (l != k) {
      t         = a[l + kn];
      a[l + kn] = a[knp1];
      a[knp1]   = t;
    }

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

    /* row elimination with column indexing */
    ax = aa;
    for (j = kp1; j <= n; ++j) {
      jn1 = j*n;
      t   = a[l + jn1];
      if (l != k) {
        a[l + jn1] = a[k + jn1];
        a[k + jn1] = t;
      }

      i__3 = n - k;
      ay   = &a[1+k+jn1];
      for (ll=0; ll<i__3; ll++) ay[ll] += t*ax[ll];
    }
  }
  ipvt[n] = n;
  if (a[n + n * n] == 0.0) {
    if (allowzeropivot) {
      PetscErrorCode ierr;
      ierr = PetscInfo1(NULL,"Zero pivot, row %D\n",n-1);CHKERRQ(ierr);
      *zeropivotdetected = PETSC_TRUE;
    } else SETERRQ1(PETSC_COMM_SELF,PETSC_ERR_MAT_LU_ZRPVT,"Zero pivot, row %D",n-1);
  }
  PetscFunctionReturn(0);
}