/*! \file
Copyright (c) 2003, The Regents of the University of California, through
Lawrence Berkeley National Laboratory (subject to receipt of any required 
approvals from U.S. Dept. of Energy) 

All rights reserved. 

The source code is distributed under BSD license, see the file License.txt
at the top-level directory.
*/

/*! @file ilu_sdrop_row.c
 * \brief Drop small rows from L
 *
 * <pre>
 * -- SuperLU routine (version 4.1) --
 * Lawrence Berkeley National Laboratory.
 * June 30, 2009
 * </pre>
 */

#include <math.h>
#include <stdlib.h>
#include "slu_sdefs.h"

extern void sswap_(int *, float [], int *, float [], int *);
extern void saxpy_(int *, float *, float [], int *, float [], int *);
extern void scopy_(int *, float [], int *, float [], int *);
extern float sasum_(int *, float *, int *);
extern float snrm2_(int *, float *, int *);
extern double dnrm2_(int *, double [], int *);
extern int isamax_(int *, float [], int *);

#if 0
static float *A;  /* used in _compare_ only */
static int _compare_(const void *a, const void *b)
{
    register int *x = (int *)a, *y = (int *)b;
    if (A[*x] - A[*y] > 0.0) return -1;
    else if (A[*x] - A[*y] < 0.0) return 1;
    else return 0;
}
#endif

/*! \brief
 * <pre>
 * Purpose
 * =======
 *    ilu_sdrop_row() - Drop some small rows from the previous 
 *    supernode (L-part only).
 * </pre>
 */
int ilu_sdrop_row(
	superlu_options_t *options, /* options */
	int    first,	    /* index of the first column in the supernode */
	int    last,	    /* index of the last column in the supernode */
	double drop_tol,    /* dropping parameter */
	int    quota,	    /* maximum nonzero entries allowed */
	int    *nnzLj,	    /* in/out number of nonzeros in L(:, 1:last) */
	double *fill_tol,   /* in/out - on exit, fill_tol=-num_zero_pivots,
			     * does not change if options->ILU_MILU != SMILU1 */
	GlobalLU_t *Glu,    /* modified */
	float swork[],   /* working space
	                     * the length of swork[] should be no less than
			     * the number of rows in the supernode */
	float swork2[], /* working space with the same size as swork[],
			     * used only by the second dropping rule */
	int    lastc	    /* if lastc == 0, there is nothing after the
			     * working supernode [first:last];
			     * if lastc == 1, there is one more column after
			     * the working supernode. */ )
{
    register int i, j, k, m1;
    register int nzlc; /* number of nonzeros in column last+1 */
    int_t xlusup_first, xlsub_first;
    int m, n; /* m x n is the size of the supernode */
    int r = 0; /* number of dropped rows */
    register float *temp;
    register float *lusup = (float *) Glu->lusup;
    int_t *lsub = Glu->lsub;
    int_t *xlsub = Glu->xlsub;
    int_t *xlusup = Glu->xlusup;
    register float d_max = 0.0, d_min = 1.0;
    int    drop_rule = options->ILU_DropRule;
    milu_t milu = options->ILU_MILU;
    norm_t nrm = options->ILU_Norm;
    float zero = 0.0;
    float one = 1.0;
    float none = -1.0;
    int i_1 = 1;
    int inc_diag; /* inc_diag = m + 1 */
    int nzp = 0;  /* number of zero pivots */
    float alpha = pow((double)(Glu->n), -1.0 / options->ILU_MILU_Dim);

    xlusup_first = xlusup[first];
    xlsub_first = xlsub[first];
    m = xlusup[first + 1] - xlusup_first;
    n = last - first + 1;
    m1 = m - 1;
    inc_diag = m + 1;
    nzlc = lastc ? (xlusup[last + 2] - xlusup[last + 1]) : 0;
    temp = swork - n;

    /* Quick return if nothing to do. */
    if (m == 0 || m == n || drop_rule == NODROP)
    {
	*nnzLj += m * n;
	return 0;
    }

    /* basic dropping: ILU(tau) */
    for (i = n; i <= m1; )
    {
	/* the average abs value of ith row */
	switch (nrm)
	{
	    case ONE_NORM:
		temp[i] = sasum_(&n, &lusup[xlusup_first + i], &m) / (double)n;
		break;
	    case TWO_NORM:
		temp[i] = snrm2_(&n, &lusup[xlusup_first + i], &m)
		    / sqrt((double)n);
		break;
	    case INF_NORM:
	    default:
		k = isamax_(&n, &lusup[xlusup_first + i], &m) - 1;
		temp[i] = fabs(lusup[xlusup_first + i + m * k]);
		break;
	}

	/* drop small entries due to drop_tol */
	if (drop_rule & DROP_BASIC && temp[i] < drop_tol)
	{
	    r++;
	    /* drop the current row and move the last undropped row here */
	    if (r > 1) /* add to last row */
	    {
		/* accumulate the sum (for MILU) */
		switch (milu)
		{
		    case SMILU_1:
		    case SMILU_2:
			saxpy_(&n, &one, &lusup[xlusup_first + i], &m,
				&lusup[xlusup_first + m - 1], &m);
			break;
		    case SMILU_3:
			for (j = 0; j < n; j++)
			    lusup[xlusup_first + (m - 1) + j * m] +=
				    fabs(lusup[xlusup_first + i + j * m]);
			break;
		    case SILU:
		    default:
			break;
		}
		scopy_(&n, &lusup[xlusup_first + m1], &m,
                       &lusup[xlusup_first + i], &m);
	    } /* if (r > 1) */
	    else /* move to last row */
	    {
		sswap_(&n, &lusup[xlusup_first + m1], &m,
			&lusup[xlusup_first + i], &m);
		if (milu == SMILU_3)
		    for (j = 0; j < n; j++) {
			lusup[xlusup_first + m1 + j * m] =
				fabs(lusup[xlusup_first + m1 + j * m]);
                    }
	    }
	    lsub[xlsub_first + i] = lsub[xlsub_first + m1];
	    m1--;
	    continue;
	} /* if dropping */
	else
	{
	    if (temp[i] > d_max) d_max = temp[i];
	    if (temp[i] < d_min) d_min = temp[i];
	}
	i++;
    } /* for */

    /* Secondary dropping: drop more rows according to the quota. */
    quota = ceil((double)quota / (double)n);
    if (drop_rule & DROP_SECONDARY && m - r > quota)
    {
	register double tol = d_max;

	/* Calculate the second dropping tolerance */
	if (quota > n)
	{
	    if (drop_rule & DROP_INTERP) /* by interpolation */
	    {
		d_max = 1.0 / d_max; d_min = 1.0 / d_min;
		tol = 1.0 / (d_max + (d_min - d_max) * quota / (m - n - r));
	    }
	    else /* by quick select */
	    {
		int len = m1 - n + 1;
		scopy_(&len, swork, &i_1, swork2, &i_1);
		tol = sqselect(len, swork2, quota - n);
#if 0
		register int *itemp = iwork - n;
		A = temp;
		for (i = n; i <= m1; i++) itemp[i] = i;
		qsort(iwork, m1 - n + 1, sizeof(int), _compare_);
		tol = temp[itemp[quota]];
#endif
	    }
	}

	for (i = n; i <= m1; )
	{
	    if (temp[i] <= tol)
	    {
		register int j;
		r++;
		/* drop the current row and move the last undropped row here */
		if (r > 1) /* add to last row */
		{
		    /* accumulate the sum (for MILU) */
		    switch (milu)
		    {
			case SMILU_1:
			case SMILU_2:
			    saxpy_(&n, &one, &lusup[xlusup_first + i], &m,
				    &lusup[xlusup_first + m - 1], &m);
			    break;
			case SMILU_3:
			    for (j = 0; j < n; j++)
				lusup[xlusup_first + (m - 1) + j * m] +=
					fabs(lusup[xlusup_first + i + j * m]);
			    break;
			case SILU:
			default:
			    break;
		    }
		    scopy_(&n, &lusup[xlusup_first + m1], &m,
			    &lusup[xlusup_first + i], &m);
		} /* if (r > 1) */
		else /* move to last row */
		{
		    sswap_(&n, &lusup[xlusup_first + m1], &m,
			    &lusup[xlusup_first + i], &m);
		    if (milu == SMILU_3)
			for (j = 0; j < n; j++) {
			    lusup[xlusup_first + m1 + j * m] =
				    fabs(lusup[xlusup_first + m1 + j * m]);
                        }
		}
		lsub[xlsub_first + i] = lsub[xlsub_first + m1];
		m1--;
		temp[i] = temp[m1];

		continue;
	    }
	    i++;

	} /* for */

    } /* if secondary dropping */

    for (i = n; i < m; i++) temp[i] = 0.0;

    if (r == 0)
    {
	*nnzLj += m * n;
	return 0;
    }

    /* add dropped entries to the diagonal */
    if (milu != SILU)
    {
	register int j;
	float t;
	float omega;
	for (j = 0; j < n; j++)
	{
	    t = lusup[xlusup_first + (m - 1) + j * m];
            if (t == zero) continue;
	    if (t > zero)
		omega = SUPERLU_MIN(2.0 * (1.0 - alpha) / t, 1.0);
	    else
		omega = SUPERLU_MAX(2.0 * (1.0 - alpha) / t, -1.0);
	    t *= omega;

 	    switch (milu)
	    {
		case SMILU_1:
		    if (t != none) {
			lusup[xlusup_first + j * inc_diag] *= (one + t);
                    }
		    else
		    {
			lusup[xlusup_first + j * inc_diag] *= *fill_tol;
#ifdef DEBUG
			printf("[1] ZERO PIVOT: FILL col %d.\n", first + j);
			fflush(stdout);
#endif
			nzp++;
		    }
		    break;
		case SMILU_2:
		    lusup[xlusup_first + j * inc_diag] *= (1.0 + fabs(t));
		    break;
		case SMILU_3:
		    lusup[xlusup_first + j * inc_diag] *= (one + t);
		    break;
		case SILU:
		default:
		    break;
	    }
	}
	if (nzp > 0) *fill_tol = -nzp;
    }

    /* Remove dropped entries from the memory and fix the pointers. */
    m1 = m - r;
    for (j = 1; j < n; j++)
    {
	register int tmp1, tmp2;
	tmp1 = xlusup_first + j * m1;
	tmp2 = xlusup_first + j * m;
	for (i = 0; i < m1; i++)
	    lusup[i + tmp1] = lusup[i + tmp2];
    }
    for (i = 0; i < nzlc; i++)
	lusup[xlusup_first + i + n * m1] = lusup[xlusup_first + i + n * m];
    for (i = 0; i < nzlc; i++)
	lsub[xlsub[last + 1] - r + i] = lsub[xlsub[last + 1] + i];
    for (i = first + 1; i <= last + 1; i++)
    {
	xlusup[i] -= r * (i - first);
	xlsub[i] -= r;
    }
    if (lastc)
    {
	xlusup[last + 2] -= r * n;
	xlsub[last + 2] -= r;
    }

    *nnzLj += (m - r) * n;
    return r;
}
