src/misc/espresso/gimpel.c

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/*
 * Revision Control Information
 *
 * $Source$
 * $Author$
 * $Revision$
 * $Date$
 *
 */
#include "mincov_int.h"


/*
 *  check for:
 *
 *              c1      c2      rest
 *              --      --      ---
 *               1       1      0 0 0 0         <-- primary row
 *               1       0      S1              <-- secondary row
 *               0       1      T1
 *               0       1      T2
 *               0       1      Tn
 *               0       0      R
 */

int
gimpel_reduce(A, select, weight, lb, bound, depth, stats, best)
sm_matrix *A;
solution_t *select;
int *weight;
int lb;
int bound;
int depth;
stats_t *stats;
solution_t **best;
{
    register sm_row *prow, *save_sec;
    register sm_col *c1, *c2;
    register sm_element *p, *p1;
    int c1_col_num, c2_col_num, primary_row_num, secondary_row_num;
    int reduce_it; 

    reduce_it = 0;
    for(prow = A->first_row; prow != 0; prow = prow->next_row) {
        if (prow->length == 2) {
            c1 = sm_get_col(A, prow->first_col->col_num);
            c2 = sm_get_col(A, prow->last_col->col_num);
            if (c1->length == 2) {
                reduce_it = 1;
            } else if (c2->length == 2) {
                c1 = sm_get_col(A, prow->last_col->col_num);
                c2 = sm_get_col(A, prow->first_col->col_num);
                reduce_it = 1;
            }
            if (reduce_it) {
                primary_row_num = prow->row_num;
                secondary_row_num = c1->first_row->row_num;
                if (secondary_row_num == primary_row_num) {
                    secondary_row_num = c1->last_row->row_num;
                }
                break;
            }
        }
    }

    if (reduce_it) {
        c1_col_num = c1->col_num;
        c2_col_num = c2->col_num;
        save_sec = sm_row_dup(sm_get_row(A, secondary_row_num));
        sm_row_remove(save_sec, c1_col_num);

        for(p = c2->first_row; p != 0; p = p->next_row) {
            if (p->row_num != primary_row_num) {
                /* merge rows S1 and T */
                for(p1 = save_sec->first_col; p1 != 0; p1 = p1->next_col) {
                    (void) sm_insert(A, p->row_num, p1->col_num);
                }
            }
        }

        sm_delcol(A, c1_col_num);
        sm_delcol(A, c2_col_num);
        sm_delrow(A, primary_row_num);
        sm_delrow(A, secondary_row_num);

        stats->gimpel_count++;
        stats->gimpel++;
        *best = sm_mincov(A, select, weight, lb-1, bound-1, depth, stats);
        stats->gimpel--;

        if (*best != NIL(solution_t)) {
            /* is secondary row covered ? */
            if (sm_row_intersects(save_sec, (*best)->row)) {
                /* yes, actually select c2 */
                solution_add(*best, weight, c2_col_num);
            } else {
                solution_add(*best, weight, c1_col_num);
            }
        }

        sm_row_free(save_sec);
        return 1;
    } else {
        return 0;
    }
}

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