GLOBAL void UMF_kernel_wrapup
(
    NumericType *Numeric,
    SymbolicType *Symbolic,
    WorkType *Work
)
{

    /* ---------------------------------------------------------------------- */
    /* local variables */
    /* ---------------------------------------------------------------------- */

    Entry pivot_value ;
    double d ;
    Entry *D ;
    Int i, k, col, row, llen, ulen, *ip, *Rperm, *Cperm, *Lilen, npiv, lp,
	*Uilen, *Lip, *Uip, *Cperm_init, up, pivrow, pivcol, *Lpos, *Upos, *Wr,
	*Wc, *Wp, *Frpos, *Fcpos, *Row_degree, *Col_degree, *Rperm_init,
	n_row, n_col, n_inner, zero_pivot, nan_pivot, n1 ;

#ifndef NDEBUG
    UMF_dump_matrix (Numeric, Work, FALSE) ;
#endif

    DEBUG0 (("Kernel complete, Starting Kernel wrapup\n")) ;
    n_row = Symbolic->n_row ;
    n_col = Symbolic->n_col ;
    n_inner = MIN (n_row, n_col) ;
    Rperm = Numeric->Rperm ;
    Cperm = Numeric->Cperm ;
    Lilen = Numeric->Lilen ;
    Uilen = Numeric->Uilen ;
    Upos = Numeric->Upos ;
    Lpos = Numeric->Lpos ;
    Lip = Numeric->Lip ;
    Uip = Numeric->Uip ;
    D = Numeric->D ;

    npiv = Work->npiv ;
    Numeric->npiv = npiv ;
    Numeric->ulen = Work->ulen ;

    ASSERT (n_row == Numeric->n_row) ;
    ASSERT (n_col == Symbolic->n_col) ;
    DEBUG0 (("Wrap-up: npiv "ID" ulen "ID"\n", npiv, Numeric->ulen)) ;
    ASSERT (npiv <= n_inner) ;

    /* this will be nonzero only if matrix is singular or rectangular */
    ASSERT (IMPLIES (npiv == n_col, Work->ulen == 0)) ;

    /* ---------------------------------------------------------------------- */
    /* find the smallest and largest entries in D */
    /* ---------------------------------------------------------------------- */

    for (k = 0 ; k < npiv ; k++)
    {
	pivot_value = D [k] ;
	ABS (d, pivot_value) ;
	zero_pivot = SCALAR_IS_ZERO (d) ;
	nan_pivot = SCALAR_IS_NAN (d) ;

	if (!zero_pivot)
	{
	    /* the pivot is nonzero, but might be Inf or NaN */
	    Numeric->nnzpiv++ ;
	}

	if (k == 0)
	{
	    Numeric->min_udiag = d ;
	    Numeric->max_udiag = d ;
	}
	else
	{
	    /* min (abs (diag (U))) behaves as follows:  If any entry is zero,
	       then the result is zero (regardless of the presence of NaN's).
	       Otherwise, if any entry is NaN, then the result is NaN.
	       Otherwise, the result is the smallest absolute value on the
	       diagonal of U.
	    */

	    if (SCALAR_IS_NONZERO (Numeric->min_udiag))
	    {
		if (zero_pivot || nan_pivot)
		{
		    Numeric->min_udiag = d ;
		}
		else if (!SCALAR_IS_NAN (Numeric->min_udiag))
		{
		    /* d and min_udiag are both non-NaN */
		    Numeric->min_udiag = MIN (Numeric->min_udiag, d) ;
		}
	    }

	    /*
	       max (abs (diag (U))) behaves as follows:  If any entry is NaN
	       then the result is NaN.  Otherise, the result is the largest
	       absolute value on the diagonal of U.
	    */

	    if (nan_pivot)
	    {
		Numeric->max_udiag = d ;
	    }
	    else if (!SCALAR_IS_NAN (Numeric->max_udiag))
	    {
		/* d and max_udiag are both non-NaN */
		Numeric->max_udiag = MAX (Numeric->max_udiag, d) ;
	    }
	}
    }

    /* ---------------------------------------------------------------------- */
    /* check if matrix is singular or rectangular */
    /* ---------------------------------------------------------------------- */

    Col_degree = Cperm ;	/* for NON_PIVOTAL_COL macro */
    Row_degree = Rperm ;	/* for NON_PIVOTAL_ROW macro */

    if (npiv < n_row)
    {
	/* finalize the row permutation */
	k = npiv ;
	DEBUGm3 (("Singular pivot rows "ID" to "ID"\n", k, n_row-1)) ;
	for (row = 0 ; row < n_row ; row++)
	{
	    if (NON_PIVOTAL_ROW (row))
	    {
		Rperm [row] = ONES_COMPLEMENT (k) ;
		DEBUGm3 (("Singular row "ID" is k: "ID" pivot row\n", row, k)) ;
		ASSERT (!NON_PIVOTAL_ROW (row)) ;
		Lpos [row] = EMPTY ;
		Uip [row] = EMPTY ;
		Uilen [row] = 0 ;
		k++ ;
	    }
	}
	ASSERT (k == n_row) ;
    }

    if (npiv < n_col)
    {
	/* finalize the col permutation */
	k = npiv ;
	DEBUGm3 (("Singular pivot cols "ID" to "ID"\n", k, n_col-1)) ;
	for (col = 0 ; col < n_col ; col++)
	{
	    if (NON_PIVOTAL_COL (col))
	    {
		Cperm [col] = ONES_COMPLEMENT (k) ;
		DEBUGm3 (("Singular col "ID" is k: "ID" pivot row\n", col, k)) ;
		ASSERT (!NON_PIVOTAL_COL (col)) ;
		Upos [col] = EMPTY ;
		Lip [col] = EMPTY ;
		Lilen [col] = 0 ;
		k++ ;
	    }
	}
	ASSERT (k == n_col) ;
    }

    if (npiv < n_inner)
    {
	/* finalize the diagonal of U */
	DEBUGm3 (("Diag of U is zero, "ID" to "ID"\n", npiv, n_inner-1)) ;
	for (k = npiv ; k < n_inner ; k++)
	{
	    CLEAR (D [k]) ;
	}
    }

    /* save the pattern of the last row of U */
    if (Numeric->ulen > 0)
    {
	DEBUGm3 (("Last row of U is not empty\n")) ;
	Numeric->Upattern = Work->Upattern ;
	Work->Upattern = (Int *) NULL ;
    }

    DEBUG2 (("Nnzpiv: "ID"  npiv "ID"\n", Numeric->nnzpiv, npiv)) ;
    ASSERT (Numeric->nnzpiv <= npiv) ;
    if (Numeric->nnzpiv < n_inner && !SCALAR_IS_NAN (Numeric->min_udiag))
    {
	/* the rest of the diagonal is zero, so min_udiag becomes 0,
	 * unless it is already NaN. */
	Numeric->min_udiag = 0.0 ;
    }

    /* ---------------------------------------------------------------------- */
    /* size n_row, n_col workspaces that can be used here: */
    /* ---------------------------------------------------------------------- */

    Frpos = Work->Frpos ;	/* of size n_row+1 */
    Fcpos = Work->Fcpos ;	/* of size n_col+1 */
    Wp = Work->Wp ;		/* of size MAX(n_row,n_col)+1 */
    /* Work->Upattern ;		cannot be used (in Numeric) */
    Wr = Work->Lpattern ;	/* of size n_row+1 */
    Wc = Work->Wrp ;		/* of size n_col+1 or bigger */

    /* ---------------------------------------------------------------------- */
    /* construct Rperm from inverse permutations */
    /* ---------------------------------------------------------------------- */

    /* use Frpos for temporary copy of inverse row permutation [ */

    for (pivrow = 0 ; pivrow < n_row ; pivrow++)
    {
	k = Rperm [pivrow] ;
	ASSERT (k < 0) ;
	k = ONES_COMPLEMENT (k) ;
	ASSERT (k >= 0 && k < n_row) ;
	Wp [k] = pivrow ;
	Frpos [pivrow] = k ;
    }
    for (k = 0 ; k < n_row ; k++)
    {
	Rperm [k] = Wp [k] ;
    }

    /* ---------------------------------------------------------------------- */
    /* construct Cperm from inverse permutation */
    /* ---------------------------------------------------------------------- */

    /* use Fcpos for temporary copy of inverse column permutation [ */

    for (pivcol = 0 ; pivcol < n_col ; pivcol++)
    {
	k = Cperm [pivcol] ;
	ASSERT (k < 0) ;
	k = ONES_COMPLEMENT (k) ;
	ASSERT (k >= 0 && k < n_col) ;
	Wp [k] = pivcol ;
	/* save a copy of the inverse column permutation in Fcpos */
	Fcpos [pivcol] = k ;
    }
    for (k = 0 ; k < n_col ; k++)
    {
	Cperm [k] = Wp [k] ;
    }

#ifndef NDEBUG
    for (k = 0 ; k < n_col ; k++)
    {
	col = Cperm [k] ;
	ASSERT (col >= 0 && col < n_col) ;
	ASSERT (Fcpos [col] == k) ;		/* col is the kth pivot */
    }
    for (k = 0 ; k < n_row ; k++)
    {
	row = Rperm [k] ;
	ASSERT (row >= 0 && row < n_row) ;
	ASSERT (Frpos [row] == k) ;		/* row is the kth pivot */
    }
#endif

#ifndef NDEBUG
    UMF_dump_lu (Numeric) ;
#endif

    /* ---------------------------------------------------------------------- */
    /* permute Lpos, Upos, Lilen, Lip, Uilen, and Uip */
    /* ---------------------------------------------------------------------- */

    for (k = 0 ; k < npiv ; k++)
    {
	pivrow = Rperm [k] ;
	Wr [k] = Uilen [pivrow] ;
	Wp [k] = Uip [pivrow] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	Uilen [k] = Wr [k] ;
	Uip [k] = Wp [k] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	pivrow = Rperm [k] ;
	Wp [k] = Lpos [pivrow] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	Lpos [k] = Wp [k] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	pivcol = Cperm [k] ;
	Wc [k] = Lilen [pivcol] ;
	Wp [k] = Lip [pivcol] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	Lilen [k] = Wc [k] ;
	Lip [k] = Wp [k] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	pivcol = Cperm [k] ;
	Wp [k] = Upos [pivcol] ;
    }

    for (k = 0 ; k < npiv ; k++)
    {
	Upos [k] = Wp [k] ;
    }

    /* ---------------------------------------------------------------------- */
    /* terminate the last Uchain and last Lchain */
    /* ---------------------------------------------------------------------- */

    Upos [npiv] = EMPTY ;
    Lpos [npiv] = EMPTY ;
    Uip [npiv] = EMPTY ;
    Lip [npiv] = EMPTY ;
    Uilen [npiv] = 0 ;
    Lilen [npiv] = 0 ;

    /* ---------------------------------------------------------------------- */
    /* convert U to the new pivot order */
    /* ---------------------------------------------------------------------- */

    n1 = Symbolic->n1 ;

    for (k = 0 ; k < n1 ; k++)
    {
	/* this is a singleton row of U */
	ulen = Uilen [k] ;
	DEBUG4 (("K "ID" New U.  ulen "ID" Singleton 1\n", k, ulen)) ;
	if (ulen > 0)
	{
	    up = Uip [k] ;
	    ip = (Int *) (Numeric->Memory + up) ;
	    for (i = 0 ; i < ulen ; i++)
	    {
		col = *ip ;
		DEBUG4 ((" old col "ID" new col "ID"\n", col, Fcpos [col]));
		ASSERT (col >= 0 && col < n_col) ;
		*ip++ = Fcpos [col] ;
	    }
	}
    }

    for (k = n1 ; k < npiv ; k++)
    {
	up = Uip [k] ;
	if (up < 0)
	{
	    /* this is the start of a new Uchain (with a pattern) */
	    ulen = Uilen [k] ;
	    DEBUG4 (("K "ID" New U.  ulen "ID" End_Uchain 1\n", k, ulen)) ;
	    if (ulen > 0)
	    {
		up = -up ;
		ip = (Int *) (Numeric->Memory + up) ;
		for (i = 0 ; i < ulen ; i++)
		{
		    col = *ip ;
		    DEBUG4 ((" old col "ID" new col "ID"\n", col, Fcpos [col]));
		    ASSERT (col >= 0 && col < n_col) ;
		    *ip++ = Fcpos [col] ;
		}
	    }
	}
    }

    ulen = Numeric->ulen ;
    if (ulen > 0)
    {
	/* convert last pivot row of U to the new pivot order */
	DEBUG4 (("K "ID" (last)\n", k)) ;
	for (i = 0 ; i < ulen ; i++)
	{
	    col = Numeric->Upattern [i] ;
	    DEBUG4 (("    old col "ID" new col "ID"\n", col, Fcpos [col])) ;
	    Numeric->Upattern [i] = Fcpos [col] ;
	}
    }

    /* Fcpos no longer needed ] */

    /* ---------------------------------------------------------------------- */
    /* convert L to the new pivot order */
    /* ---------------------------------------------------------------------- */

    for (k = 0 ; k < n1 ; k++)
    {
	llen = Lilen [k] ;
	DEBUG4 (("K "ID" New L.  llen "ID" Singleton col\n", k, llen)) ;
	if (llen > 0)
	{
	    lp = Lip [k] ;
	    ip = (Int *) (Numeric->Memory + lp) ;
	    for (i = 0 ; i < llen ; i++)
	    {
		row = *ip ;
		DEBUG4 (("    old row "ID" new row "ID"\n", row, Frpos [row])) ;
		ASSERT (row >= 0 && row < n_row) ;
		*ip++ = Frpos [row] ;
	    }
	}
    }

    for (k = n1 ; k < npiv ; k++)
    {
	llen = Lilen [k] ;
	DEBUG4 (("K "ID" New L.  llen "ID" \n", k, llen)) ;
	if (llen > 0)
	{
	    lp = Lip [k] ;
	    if (lp < 0)
	    {
		/* this starts a new Lchain */
		lp = -lp ;
	    }
	    ip = (Int *) (Numeric->Memory + lp) ;
	    for (i = 0 ; i < llen ; i++)
	    {
		row = *ip ;
		DEBUG4 (("    old row "ID" new row "ID"\n", row, Frpos [row])) ;
		ASSERT (row >= 0 && row < n_row) ;
		*ip++ = Frpos [row] ;
	    }
	}
    }

    /* Frpos no longer needed ] */

    /* ---------------------------------------------------------------------- */
    /* combine symbolic and numeric permutations */
    /* ---------------------------------------------------------------------- */

    Cperm_init = Symbolic->Cperm_init ;
    Rperm_init = Symbolic->Rperm_init ;

    for (k = 0 ; k < n_row ; k++)
    {
	Rperm [k] = Rperm_init [Rperm [k]] ;
    }

    for (k = 0 ; k < n_col ; k++)
    {
	Cperm [k] = Cperm_init [Cperm [k]] ;
    }

    /* Work object will be freed immediately upon return (to UMF_kernel */
    /* and then to UMFPACK_numeric). */
}
Exemple #2
0
GLOBAL Int UMF_row_search
(
    NumericType *Numeric,
    WorkType *Work,
    SymbolicType *Symbolic,
    Int cdeg0,			/* length of column in Front */
    Int cdeg1,			/* length of column outside Front */
    const Int Pattern [ ],	/* pattern of column, Pattern [0..cdeg1 -1] */
    const Int Pos [ ],		/* Pos [Pattern [0..cdeg1 -1]] = 0..cdeg1 -1 */
    Int pivrow [2],		/* pivrow [IN] and pivrow [OUT] */
    Int rdeg [2],		/* rdeg [IN] and rdeg [OUT] */
    Int W_i [ ],		/* pattern of pivrow [IN], */
				/* either Fcols or Woi */
    Int W_o [ ],		/* pattern of pivrow [OUT], */
				/* either Wio or Woo */
    Int prior_pivrow [2],	/* the two other rows just scanned, if any */
    const Entry Wxy [ ],	/* numerical values Wxy [0..cdeg1-1],
				   either Wx or Wy */

    Int pivcol,			/* the candidate column being searched */
    Int freebie [ ]
)
{

    /* ---------------------------------------------------------------------- */
    /* local variables */
    /* ---------------------------------------------------------------------- */

    double maxval, toler, toler2, value, pivot [2] ;
    Int i, row, deg, col, *Frpos, fnrows, *E, j, ncols, *Cols, *Rows,
	e, f, Wrpflag, *Fcpos, fncols, tpi, max_rdeg, nans_in_col, was_offdiag,
	diag_row, prefer_diagonal, *Wrp, found, *Diagonal_map ;
    Tuple *tp, *tpend, *tp1, *tp2 ;
    Unit *Memory, *p ;
    Element *ep ;
    Int *Row_tuples, *Row_degree, *Row_tlen ;

#ifndef NDEBUG
    Int *Col_degree ;
    DEBUG2 (("Row_search:\n")) ;
    for (i = 0 ; i < cdeg1 ; i++)
    {
	row = Pattern [i] ;
	DEBUG4 (("   row: "ID"\n", row)) ;
	ASSERT (row >= 0 && row < Numeric->n_row) ;
	ASSERT (i == Pos [row]) ;
    }
    /* If row is not in Pattern [0..cdeg1-1], then Pos [row] == EMPTY */
    if (UMF_debug > 0 || Numeric->n_row < 1000)
    {
	Int cnt = cdeg1 ;
	DEBUG4 (("Scan all rows:\n")) ;
	for (row = 0 ; row < Numeric->n_row ; row++)
	{
	    if (Pos [row] < 0)
	    {
		cnt++ ;
	    }
	    else
	    {
		DEBUG4 (("   row: "ID" pos "ID"\n", row, Pos [row])) ;
	    }
	}
	ASSERT (cnt == Numeric->n_row) ;
    }
    Col_degree = Numeric->Cperm ;   /* for NON_PIVOTAL_COL macro only */
    ASSERT (pivcol >= 0 && pivcol < Work->n_col) ;
    ASSERT (NON_PIVOTAL_COL (pivcol)) ;
#endif

    pivot [IN] = 0. ;
    pivot [OUT] = 0. ;

    /* ---------------------------------------------------------------------- */
    /* get parameters */
    /* ---------------------------------------------------------------------- */

    Row_degree = Numeric->Rperm ;
    Row_tuples = Numeric->Uip ;
    Row_tlen   = Numeric->Uilen ;
    Wrp = Work->Wrp ;
    Frpos = Work->Frpos ;
    E = Work->E ;
    Memory = Numeric->Memory ;
    fnrows = Work->fnrows ;

    prefer_diagonal = Symbolic->prefer_diagonal ;
    Diagonal_map = Work->Diagonal_map ;

    if (Diagonal_map)
    {
	diag_row = Diagonal_map [pivcol] ;
	was_offdiag = diag_row < 0 ;
	if (was_offdiag)
	{
	    /* the "diagonal" entry in this column was permuted here by an
	     * earlier pivot choice.  The tighter off-diagonal tolerance will
	     * be used instead of the symmetric tolerance. */
	    diag_row = FLIP (diag_row) ;
	}
	ASSERT (diag_row >= 0 && diag_row < Numeric->n_row) ;
    }
    else
    {
	diag_row = EMPTY ;	/* unused */
	was_offdiag = EMPTY ;	/* unused */
    }

    /* pivot row degree cannot exceed max_rdeg */
    max_rdeg = Work->fncols_max ;

    /* ---------------------------------------------------------------------- */
    /* scan pivot column for candidate rows */
    /* ---------------------------------------------------------------------- */

    maxval = 0.0 ;
    nans_in_col = FALSE ;

    for (i = 0 ; i < cdeg1 ; i++)
    {
	APPROX_ABS (value, Wxy [i]) ;
	if (SCALAR_IS_NAN (value))
	{
	    nans_in_col = TRUE ;
	    maxval = value ;
	    break ;
	}
	/* This test can now ignore the NaN case: */
	maxval = MAX (maxval, value) ;
    }

    /* if maxval is zero, the matrix is numerically singular */

    toler = Numeric->relpt * maxval ;
    toler2 = Numeric->relpt2 * maxval ;
    toler2 = was_offdiag ? toler : toler2 ;

    DEBUG5 (("Row_search begins [ maxval %g toler %g %g\n",
	maxval, toler, toler2)) ;
    if (SCALAR_IS_NAN (toler) || SCALAR_IS_NAN (toler2))
    {
	nans_in_col = TRUE ;
    }

    if (!nans_in_col)
    {

	/* look for the diagonal entry, if it exists */
	found = FALSE ;
	ASSERT (!SCALAR_IS_NAN (toler)) ;

	if (prefer_diagonal)
	{
	    ASSERT (diag_row != EMPTY) ;
	    i = Pos [diag_row] ;
	    if (i >= 0)
	    {
		double a ;
		ASSERT (i < cdeg1) ;
		ASSERT (diag_row == Pattern [i]) ;

		APPROX_ABS (a, Wxy [i]) ;

		ASSERT (!SCALAR_IS_NAN (a)) ;
		ASSERT (!SCALAR_IS_NAN (toler2)) ;

		if (SCALAR_IS_NONZERO (a) && a >= toler2)
		{
		    /* found it! */
		    DEBUG3 (("Symmetric pivot: "ID" "ID"\n", pivcol, diag_row));
		    found = TRUE ;
		    if (Frpos [diag_row] >= 0 && Frpos [diag_row] < fnrows)
		    {
			pivrow [IN] = diag_row ;
			pivrow [OUT] = EMPTY ;
		    }
		    else
		    {
			pivrow [IN] = EMPTY ;
			pivrow [OUT] = diag_row ;
		    }
		}
	    }
	}

	/* either no diagonal found, or we didn't look for it */
	if (!found)
	{
	    if (cdeg0 > 0)
	    {

		/* this is a column in the front */
		for (i = 0 ; i < cdeg0 ; i++)
		{
		    double a ;
		    APPROX_ABS (a, Wxy [i]) ;
		    ASSERT (!SCALAR_IS_NAN (a)) ;
		    ASSERT (!SCALAR_IS_NAN (toler)) ;
		    if (SCALAR_IS_NONZERO (a) && a >= toler)
		    {
			row = Pattern [i] ;
			deg = Row_degree [row] ;
#ifndef NDEBUG
			DEBUG6 ((ID" candidate row "ID" deg "ID" absval %g\n",
			    i, row, deg, a)) ;
			UMF_dump_rowcol (0, Numeric, Work, row, TRUE) ;
#endif
			ASSERT (Frpos [row] >= 0 && Frpos [row] < fnrows) ;
			ASSERT (Frpos [row] == i) ;
			/* row is in the current front */
			DEBUG4 ((" in front\n")) ;
			if (deg < rdeg [IN]
			    /* break ties by picking the largest entry: */
			       || (deg == rdeg [IN] && a > pivot [IN])
			    /* break ties by picking the diagonal entry: */
			    /* || (deg == rdeg [IN] && row == diag_row) */
			   )
			{
			    /* best row in front, so far */
			    pivrow [IN] = row ;
			    rdeg [IN] = deg ;
			    pivot [IN] = a ;
			}
		    }
		}
		for ( ; i < cdeg1 ; i++)
		{
		    double a ;
		    APPROX_ABS (a, Wxy [i]) ;
		    ASSERT (!SCALAR_IS_NAN (a)) ;
		    ASSERT (!SCALAR_IS_NAN (toler)) ;
		    if (SCALAR_IS_NONZERO (a) && a >= toler)
		    {
			row = Pattern [i] ;
			deg = Row_degree [row] ;
#ifndef NDEBUG
			DEBUG6 ((ID" candidate row "ID" deg "ID" absval %g\n",
			    i, row, deg, a)) ;
			UMF_dump_rowcol (0, Numeric, Work, row, TRUE) ;
#endif
			ASSERT (Frpos [row] == i) ;
			/* row is not in the current front */
			DEBUG4 ((" NOT in front\n")) ;
			if (deg < rdeg [OUT]
			    /* break ties by picking the largest entry: */
			       || (deg == rdeg [OUT] && a > pivot [OUT])
			    /* break ties by picking the diagonal entry: */
			    /* || (deg == rdeg [OUT] && row == diag_row) */
			   )
			{
			    /* best row not in front, so far */
			    pivrow [OUT] = row ;
			    rdeg [OUT] = deg ;
			    pivot [OUT] = a ;
			}
		    }
		}

	    }
	    else
	    {

		/* this column is not in the front */
		for (i = 0 ; i < cdeg1 ; i++)
		{
		    double a ;
		    APPROX_ABS (a, Wxy [i]) ;
		    ASSERT (!SCALAR_IS_NAN (a)) ;
		    ASSERT (!SCALAR_IS_NAN (toler)) ;
		    if (SCALAR_IS_NONZERO (a) && a >= toler)
		    {
			row = Pattern [i] ;
			deg = Row_degree [row] ;
#ifndef NDEBUG
			DEBUG6 ((ID" candidate row "ID" deg "ID" absval %g\n",
			    i, row, deg, a)) ;
			UMF_dump_rowcol (0, Numeric, Work, row, TRUE) ;
#endif
			if (Frpos [row] >= 0 && Frpos [row] < fnrows)
			{
			    /* row is in the current front */
			    DEBUG4 ((" in front\n")) ;
			    if (deg < rdeg [IN]
			    /* break ties by picking the largest entry: */
			       || (deg == rdeg [IN] && a > pivot [IN])
			    /* break ties by picking the diagonal entry: */
			    /* || (deg == rdeg [IN] && row == diag_row) */
			       )
			    {
				/* best row in front, so far */
				pivrow [IN] = row ;
				rdeg [IN] = deg ;
				pivot [IN] = a ;
			    }
			}
			else
			{
			    /* row is not in the current front */
			    DEBUG4 ((" NOT in front\n")) ;
			    if (deg < rdeg [OUT]
			    /* break ties by picking the largest entry: */
			       || (deg == rdeg[OUT] && a > pivot [OUT])
			    /* break ties by picking the diagonal entry: */
			    /* || (deg == rdeg[OUT] && row == diag_row) */
			       )
			    {
				/* best row not in front, so far */
				pivrow [OUT] = row ;
				rdeg [OUT] = deg ;
				pivot [OUT] = a ;
			    }
			}
		    }
		}
	    }
	}
    }

    /* ---------------------------------------------------------------------- */
    /* NaN handling */
    /* ---------------------------------------------------------------------- */

    /* if cdeg1 > 0 then we must have found a pivot row ... unless NaN's */
    /* exist.  Try with no numerical tests if no pivot found. */

    if (cdeg1 > 0 && pivrow [IN] == EMPTY && pivrow [OUT] == EMPTY)
    {
	/* cleanup for the NaN case */
	DEBUG0 (("Found a NaN in pivot column!\n")) ;

	/* grab the first entry in the pivot column, ignoring degree, */
	/* numerical stability, and symmetric preference */
	row = Pattern [0] ;
	deg = Row_degree [row] ;
	if (Frpos [row] >= 0 && Frpos [row] < fnrows)
	{
	    /* row is in the current front */
	    DEBUG4 ((" in front\n")) ;
	    pivrow [IN] = row ;
	    rdeg [IN] = deg ;
	}
	else
	{
	    /* row is not in the current front */
	    DEBUG4 ((" NOT in front\n")) ;
	    pivrow [OUT] = row ;
	    rdeg [OUT] = deg ;
	}

	/* We are now guaranteed to have a pivot, no matter how broken */
	/* (non-IEEE compliant) the underlying numerical operators are. */
	/* This is particularly a problem for Microsoft compilers (they do */
	/* not handle NaN's properly). Now try to find a sparser pivot, if */
	/* possible. */

	for (i = 1 ; i < cdeg1 ; i++)
	{
	    row = Pattern [i] ;
	    deg = Row_degree [row] ;

	    if (Frpos [row] >= 0 && Frpos [row] < fnrows)
	    {
		/* row is in the current front */
		DEBUG4 ((" in front\n")) ;
		if (deg < rdeg [IN] || (deg == rdeg [IN] && row == diag_row))
		{
		    /* best row in front, so far */
		    pivrow [IN] = row ;
		    rdeg [IN] = deg ;
		}
	    }
	    else
	    {
		/* row is not in the current front */
		DEBUG4 ((" NOT in front\n")) ;
		if (deg < rdeg [OUT] || (deg == rdeg [OUT] && row == diag_row))
		{
		    /* best row not in front, so far */
		    pivrow [OUT] = row ;
		    rdeg [OUT] = deg ;
		}
	    }
	}
    }

    /* We found a pivot if there are entries (even zero ones) in pivot col */
    ASSERT (IMPLIES (cdeg1 > 0, pivrow[IN] != EMPTY || pivrow[OUT] != EMPTY)) ;

    /* If there are no entries in the pivot column, then no pivot is found */
    ASSERT (IMPLIES (cdeg1 == 0, pivrow[IN] == EMPTY && pivrow[OUT] == EMPTY)) ;

    /* ---------------------------------------------------------------------- */
    /* check for singular matrix */
    /* ---------------------------------------------------------------------- */

    if (cdeg1  == 0)
    {
	if (fnrows > 0)
	{
	    /*
		Get the pivrow [OUT][IN] from the current front.
		The frontal matrix looks like this:

			pivcol[OUT]
			|
			v
		x x x x 0   <- so grab this row as the pivrow [OUT][IN].
		x x x x 0
		x x x x 0
		0 0 0 0 0

		The current frontal matrix has some rows in it.  The degree
		of the pivcol[OUT] is zero.  The column is empty, and the
		current front does not contribute to it.

	    */
	    pivrow [IN] = Work->Frows [0] ;
	    DEBUGm4 (("Got zero pivrow[OUT][IN] "ID" from current front\n",
		pivrow [IN])) ;
	}
	else
	{

	    /*
		Get a pivot row from the row-merge tree, use as
		pivrow [OUT][OUT].   pivrow [IN] remains EMPTY.
		This can only happen if the current front is 0-by-0.
	    */

	    Int *Front_leftmostdesc, *Front_1strow, *Front_new1strow, row1,
		row2, fleftmost, nfr, n_row, frontid ;

	    ASSERT (Work->fncols == 0) ;

	    Front_leftmostdesc = Symbolic->Front_leftmostdesc ;
	    Front_1strow = Symbolic->Front_1strow ;
	    Front_new1strow = Work->Front_new1strow ;
	    nfr = Symbolic->nfr ;
	    n_row = Numeric->n_row ;
	    frontid = Work->frontid ;

	    DEBUGm4 (("Note: pivcol: "ID" is empty front "ID"\n",
		pivcol, frontid)) ;
#ifndef NDEBUG
	    DEBUG1 (("Calling dump rowmerge\n")) ;
	    UMF_dump_rowmerge (Numeric, Symbolic, Work) ;
#endif

	    /* Row-merge set is the non-pivotal rows in the range */
	    /* Front_new1strow [Front_leftmostdesc [frontid]] to */
	    /* Front_1strow [frontid+1] - 1. */
	    /* If this is empty, then use the empty rows, in the range */
	    /* Front_new1strow [nfr] to n_row-1. */
	    /* If this too is empty, then pivrow [OUT] will be empty. */
	    /* In both cases, update Front_new1strow [...]. */

	    fleftmost = Front_leftmostdesc [frontid] ;
	    row1 = Front_new1strow [fleftmost] ;
	    row2 = Front_1strow [frontid+1] - 1 ;
	    DEBUG1 (("Leftmost: "ID" Rows ["ID" to "ID"] srch ["ID" to "ID"]\n",
		fleftmost, Front_1strow [frontid], row2, row1, row2)) ;

	    /* look in the range row1 ... row2 */
	    for (row = row1 ; row <= row2 ; row++)
	    {
		DEBUG3 (("   Row: "ID"\n", row)) ;
		if (NON_PIVOTAL_ROW (row))
		{
		    /* found it */
		    DEBUG3 (("   Row: "ID" found\n", row)) ;
		    ASSERT (Frpos [row] == EMPTY) ;
		    pivrow [OUT] = row ;
		    DEBUGm4 (("got row merge pivrow %d\n", pivrow [OUT])) ;
		    break ;
		}
	    }
	    Front_new1strow [fleftmost] = row ;

	    if (pivrow [OUT] == EMPTY)
	    {
		/* not found, look in empty row set in "dummy" front */
		row1 = Front_new1strow [nfr] ;
		row2 = n_row-1 ;
		DEBUG3 (("Empty: "ID" Rows ["ID" to "ID"] srch["ID" to "ID"]\n",
		    nfr, Front_1strow [nfr], row2, row1, row2)) ;

		/* look in the range row1 ... row2 */
		for (row = row1 ; row <= row2 ; row++)
		{
		    DEBUG3 (("   Empty Row: "ID"\n", row)) ;
		    if (NON_PIVOTAL_ROW (row))
		    {
			/* found it */
			DEBUG3 (("   Empty Row: "ID" found\n", row)) ;
			ASSERT (Frpos [row] == EMPTY) ;
			pivrow [OUT] = row ;
			DEBUGm4 (("got dummy row pivrow %d\n", pivrow [OUT])) ;
			break ;
		    }
		}
		Front_new1strow [nfr] = row ;
	    }

	    if (pivrow [OUT] == EMPTY)
	    {
		/* Row-merge set is empty.  We can just discard */
		/* the candidate pivot column. */
		DEBUG0 (("Note: row-merge set empty\n")) ;
		DEBUGm4 (("got no pivrow \n")) ;
		return (UMFPACK_WARNING_singular_matrix) ;
	    }
	}
    }

    /* ---------------------------------------------------------------------- */
    /* construct the candidate row in the front, if any */
    /* ---------------------------------------------------------------------- */

#ifndef NDEBUG
    /* check Wrp */
    ASSERT (Work->Wrpflag > 0) ;
    if (UMF_debug > 0 || Work->n_col < 1000)
    {
	for (i = 0 ; i < Work->n_col ; i++)
	{
	    ASSERT (Wrp [i] < Work->Wrpflag) ;
	}
    }
#endif

#ifndef NDEBUG
    DEBUG4 (("pivrow [IN]: "ID"\n", pivrow [IN])) ;
    UMF_dump_rowcol (0, Numeric, Work, pivrow [IN], TRUE) ;
#endif

    if (pivrow [IN] != EMPTY)
    {

	/* the row merge candidate row is not pivrow [IN] */
	freebie [IN] = (pivrow [IN] == prior_pivrow [IN]) && (cdeg1  > 0) ;
	ASSERT (cdeg1  >= 0) ;

	if (!freebie [IN])
	{
	    /* include current front in the degree of this row */

	    Fcpos = Work->Fcpos ;
	    fncols = Work->fncols ;

	    Wrpflag = Work->Wrpflag ;

	    /* -------------------------------------------------------------- */
	    /* construct the pattern of the IN row */
	    /* -------------------------------------------------------------- */

#ifndef NDEBUG
	    /* check Fcols */
	    DEBUG5 (("ROW ASSEMBLE: rdeg "ID"\nREDUCE ROW "ID"\n",
		fncols, pivrow [IN])) ;
	    for (j = 0 ; j < fncols ; j++)
	    {
		col = Work->Fcols [j] ;
		ASSERT (col >= 0 && col < Work->n_col) ;
		ASSERT (Fcpos [col] >= 0) ;
	    }
	    if (UMF_debug > 0 || Work->n_col < 1000)
	    {
		Int cnt = fncols ;
		for (col = 0 ; col < Work->n_col ; col++)
		{
		    if (Fcpos [col] < 0) cnt++ ;
		}
		ASSERT (cnt == Work->n_col) ;
	    }
#endif

	    rdeg [IN] = fncols ;

	    ASSERT (pivrow [IN] >= 0 && pivrow [IN] < Work->n_row) ;
	    ASSERT (NON_PIVOTAL_ROW (pivrow [IN])) ;

	    /* add the pivot column itself */
	    ASSERT (Wrp [pivcol] != Wrpflag) ;
	    if (Fcpos [pivcol] < 0)
	    {
		DEBUG3 (("Adding pivot col to pivrow [IN] pattern\n")) ;
		if (rdeg [IN] >= max_rdeg)
		{
		    /* :: pattern change (in) :: */
		    return (UMFPACK_ERROR_different_pattern) ;
		}
		Wrp [pivcol] = Wrpflag ;
		W_i [rdeg [IN]++] = pivcol ;
	    }

	    tpi = Row_tuples [pivrow [IN]] ;
	    if (tpi)
	    {
		tp = (Tuple *) (Memory + tpi) ;
		tp1 = tp ;
		tp2 = tp ;
		tpend = tp + Row_tlen [pivrow [IN]] ;
		for ( ; tp < tpend ; tp++)
		{
		    e = tp->e ;
		    ASSERT (e > 0 && e <= Work->nel) ;
		    if (!E [e])
		    {
			continue ;	/* element already deallocated */
		    }
		    f = tp->f ;
		    p = Memory + E [e] ;
		    ep = (Element *) p ;
		    p += UNITS (Element, 1) ;
		    Cols = (Int *) p ;
		    ncols = ep->ncols ;
		    Rows = Cols + ncols ;
		    if (Rows [f] == EMPTY)
		    {
			continue ;	/* row already assembled */
		    }
		    ASSERT (pivrow [IN] == Rows [f]) ;

		    for (j = 0 ; j < ncols ; j++)
		    {
			col = Cols [j] ;
			ASSERT (col >= EMPTY && col < Work->n_col) ;
			if ((col >= 0) && (Wrp [col] != Wrpflag)
			    && Fcpos [col] <0)
			{
			    ASSERT (NON_PIVOTAL_COL (col)) ;
			    if (rdeg [IN] >= max_rdeg)
			    {
				/* :: pattern change (rdeg in failure) :: */
				DEBUGm4 (("rdeg [IN] >= max_rdeg failure\n")) ;
				return (UMFPACK_ERROR_different_pattern) ;
			    }
			    Wrp [col] = Wrpflag ;
			    W_i [rdeg [IN]++] = col ;
			}
		    }

		    *tp2++ = *tp ;	/* leave the tuple in the list */
		}
		Row_tlen [pivrow [IN]] = tp2 - tp1 ;
	    }

#ifndef NDEBUG
	    DEBUG4 (("Reduced IN row:\n")) ;
	    for (j = 0 ; j < fncols ; j++)
	    {
		DEBUG6 ((" "ID" "ID" "ID"\n",
		    j, Work->Fcols [j], Fcpos [Work->Fcols [j]])) ;
		ASSERT (Fcpos [Work->Fcols [j]] >= 0) ;
	    }
	    for (j = fncols ; j < rdeg [IN] ; j++)
	    {
		DEBUG6 ((" "ID" "ID" "ID"\n", j, W_i [j], Wrp [W_i [j]]));
		ASSERT (W_i [j] >= 0 && W_i [j] < Work->n_col) ;
		ASSERT (Wrp [W_i [j]] == Wrpflag) ;
	    }
	    /* mark the end of the pattern in case we scan it by mistake */
	    /* Note that this means W_i must be of size >= fncols_max + 1 */
	    W_i [rdeg [IN]] = EMPTY ;
#endif

	    /* rdeg [IN] is now the exact degree of the IN row */

	    /* clear Work->Wrp. */
	    Work->Wrpflag++ ;
	    /* All Wrp [0..n_col] is now < Wrpflag */
	}
    }

#ifndef NDEBUG
    /* check Wrp */
    if (UMF_debug > 0 || Work->n_col < 1000)
    {
	for (i = 0 ; i < Work->n_col ; i++)
	{
	    ASSERT (Wrp [i] < Work->Wrpflag) ;
	}
    }
#endif

    /* ---------------------------------------------------------------------- */
    /* construct the candidate row not in the front, if any */
    /* ---------------------------------------------------------------------- */

#ifndef NDEBUG
    DEBUG4 (("pivrow [OUT]: "ID"\n", pivrow [OUT])) ;
    UMF_dump_rowcol (0, Numeric, Work, pivrow [OUT], TRUE) ;
#endif

    /* If this is a candidate row from the row merge set, force it to be */
    /* scanned (ignore prior_pivrow [OUT]). */

    if (pivrow [OUT] != EMPTY)
    {
	freebie [OUT] = (pivrow [OUT] == prior_pivrow [OUT]) && cdeg1  > 0 ;
	ASSERT (cdeg1  >= 0) ;

	if (!freebie [OUT])
	{

	    Wrpflag = Work->Wrpflag ;

	    /* -------------------------------------------------------------- */
	    /* construct the pattern of the row */
	    /* -------------------------------------------------------------- */

	    rdeg [OUT] = 0 ;

	    ASSERT (pivrow [OUT] >= 0 && pivrow [OUT] < Work->n_row) ;
	    ASSERT (NON_PIVOTAL_ROW (pivrow [OUT])) ;

	    /* add the pivot column itself */
	    ASSERT (Wrp [pivcol] != Wrpflag) ;
	    DEBUG3 (("Adding pivot col to pivrow [OUT] pattern\n")) ;
	    if (rdeg [OUT] >= max_rdeg)
	    {
		/* :: pattern change (out) :: */
		return (UMFPACK_ERROR_different_pattern) ;
	    }
	    Wrp [pivcol] = Wrpflag ;
	    W_o [rdeg [OUT]++] = pivcol ;

	    tpi = Row_tuples [pivrow [OUT]] ;
	    if (tpi)
	    {
		tp = (Tuple *) (Memory + tpi) ;
		tp1 = tp ;
		tp2 = tp ;
		tpend = tp + Row_tlen [pivrow [OUT]] ;
		for ( ; tp < tpend ; tp++)
		{
		    e = tp->e ;
		    ASSERT (e > 0 && e <= Work->nel) ;
		    if (!E [e])
		    {
			continue ;	/* element already deallocated */
		    }
		    f = tp->f ;
		    p = Memory + E [e] ;
		    ep = (Element *) p ;
		    p += UNITS (Element, 1) ;
		    Cols = (Int *) p ;
		    ncols = ep->ncols ;
		    Rows = Cols + ncols ;
		    if (Rows [f] == EMPTY)
		    {
			continue ;	/* row already assembled */
		    }
		    ASSERT (pivrow [OUT] == Rows [f]) ;

		    for (j = 0 ; j < ncols ; j++)
		    {
			col = Cols [j] ;
			ASSERT (col >= EMPTY && col < Work->n_col) ;
			if ((col >= 0) && (Wrp [col] != Wrpflag))
			{
			    ASSERT (NON_PIVOTAL_COL (col)) ;
			    if (rdeg [OUT] >= max_rdeg)
			    {
				/* :: pattern change (rdeg out failure) :: */
				DEBUGm4 (("rdeg [OUT] failure\n")) ;
				return (UMFPACK_ERROR_different_pattern) ;
			    }
			    Wrp [col] = Wrpflag ;
			    W_o [rdeg [OUT]++] = col ;
			}
		    }
		    *tp2++ = *tp ;	/* leave the tuple in the list */
		}
		Row_tlen [pivrow [OUT]] = tp2 - tp1 ;
	    }

#ifndef NDEBUG
	    DEBUG4 (("Reduced row OUT:\n")) ;
	    for (j = 0 ; j < rdeg [OUT] ; j++)
	    {
		DEBUG6 ((" "ID" "ID" "ID"\n", j, W_o [j], Wrp [W_o [j]])) ;
		ASSERT (W_o [j] >= 0 && W_o [j] < Work->n_col) ;
		ASSERT (Wrp [W_o [j]] == Wrpflag) ;
	    }
	    /* mark the end of the pattern in case we scan it by mistake */
	    /* Note that this means W_o must be of size >= fncols_max + 1 */
	    W_o [rdeg [OUT]] = EMPTY ;
#endif

	    /* rdeg [OUT] is now the exact degree of the row */

	    /* clear Work->Wrp. */
	    Work->Wrpflag++ ;
	    /* All Wrp [0..n] is now < Wrpflag */

	}

    }
    DEBUG5 (("Row_search end ] \n")) ;

#ifndef NDEBUG
    /* check Wrp */
    if (UMF_debug > 0 || Work->n_col < 1000)
    {
	for (i = 0 ; i < Work->n_col ; i++)
	{
	    ASSERT (Wrp [i] < Work->Wrpflag) ;
	}
    }
#endif

    return (UMFPACK_OK) ;
}