introduce schedule tree representation

[isl.git] / basis_reduction_templ.c

/*
 * Copyright 2006-2007 Universiteit Leiden
 * Copyright 2008-2009 Katholieke Universiteit Leuven
 *
 * Use of this software is governed by the MIT license
 *
 * Written by Sven Verdoolaege, Leiden Institute of Advanced Computer Science,
 * Universiteit Leiden, Niels Bohrweg 1, 2333 CA Leiden, The Netherlands
 * and K.U.Leuven, Departement Computerwetenschappen, Celestijnenlaan 200A,
 * B-3001 Leuven, Belgium
 */

#include <stdlib.h>
#include <isl_ctx_private.h>
#include <isl_map_private.h>
#include <isl_vec_private.h>
#include <isl_options_private.h>
#include "isl_basis_reduction.h"

static void save_alpha(GBR_LP *lp, int first, int n, GBR_type *alpha)
{
        int i;

        for (i = 0; i < n; ++i)
                GBR_lp_get_alpha(lp, first + i, &alpha[i]);
}

/* Compute a reduced basis for the set represented by the tableau "tab".
 * tab->basis, which must be initialized by the calling function to an affine
 * unimodular basis, is updated to reflect the reduced basis.
 * The first tab->n_zero rows of the basis (ignoring the constant row)
 * are assumed to correspond to equalities and are left untouched.
 * tab->n_zero is updated to reflect any additional equalities that
 * have been detected in the first rows of the new basis.
 * The final tab->n_unbounded rows of the basis are assumed to correspond
 * to unbounded directions and are also left untouched.
 * In particular this means that the remaining rows are assumed to
 * correspond to bounded directions.
 *
 * This function implements the algorithm described in
 * "An Implementation of the Generalized Basis Reduction Algorithm
 *  for Integer Programming" of Cook el al. to compute a reduced basis.
 * We use \epsilon = 1/4.
 *
 * If ctx->opt->gbr_only_first is set, the user is only interested
 * in the first direction.  In this case we stop the basis reduction when
 * the width in the first direction becomes smaller than 2.
 */
struct isl_tab *isl_tab_compute_reduced_basis(struct isl_tab *tab)
{
        unsigned dim;
        struct isl_ctx *ctx;
        struct isl_mat *B;
        int unbounded;
        int i;
        GBR_LP *lp = NULL;
        GBR_type F_old, alpha, F_new;
        int row;
        isl_int tmp;
        struct isl_vec *b_tmp;
        GBR_type *F = NULL;
        GBR_type *alpha_buffer[2] = { NULL, NULL };
        GBR_type *alpha_saved;
        GBR_type F_saved;
        int use_saved = 0;
        isl_int mu[2];
        GBR_type mu_F[2];
        GBR_type two;
        GBR_type one;
        int empty = 0;
        int fixed = 0;
        int fixed_saved = 0;
        int mu_fixed[2];
        int n_bounded;
        int gbr_only_first;

        if (!tab)
                return NULL;

        if (tab->empty)
                return tab;

        ctx = tab->mat->ctx;
        gbr_only_first = ctx->opt->gbr_only_first;
        dim = tab->n_var;
        B = tab->basis;
        if (!B)
                return tab;

        n_bounded = dim - tab->n_unbounded;
        if (n_bounded <= tab->n_zero + 1)
                return tab;

        isl_int_init(tmp);
        isl_int_init(mu[0]);
        isl_int_init(mu[1]);

        GBR_init(alpha);
        GBR_init(F_old);
        GBR_init(F_new);
        GBR_init(F_saved);
        GBR_init(mu_F[0]);
        GBR_init(mu_F[1]);
        GBR_init(two);
        GBR_init(one);

        b_tmp = isl_vec_alloc(ctx, dim);
        if (!b_tmp)
                goto error;

        F = isl_alloc_array(ctx, GBR_type, n_bounded);
        alpha_buffer[0] = isl_alloc_array(ctx, GBR_type, n_bounded);
        alpha_buffer[1] = isl_alloc_array(ctx, GBR_type, n_bounded);
        alpha_saved = alpha_buffer[0];

        if (!F || !alpha_buffer[0] || !alpha_buffer[1])
                goto error;

        for (i = 0; i < n_bounded; ++i) {
                GBR_init(F[i]);
                GBR_init(alpha_buffer[0][i]);
                GBR_init(alpha_buffer[1][i]);
        }

        GBR_set_ui(two, 2);
        GBR_set_ui(one, 1);

        lp = GBR_lp_init(tab);
        if (!lp)
                goto error;

        i = tab->n_zero;

        GBR_lp_set_obj(lp, B->row[1+i]+1, dim);
        ctx->stats->gbr_solved_lps++;
        unbounded = GBR_lp_solve(lp);
        isl_assert(ctx, !unbounded, goto error);
        GBR_lp_get_obj_val(lp, &F[i]);

        if (GBR_lt(F[i], one)) {
                if (!GBR_is_zero(F[i])) {
                        empty = GBR_lp_cut(lp, B->row[1+i]+1);
                        if (empty)
                                goto done;
                        GBR_set_ui(F[i], 0);
                }
                tab->n_zero++;
        }

        do {
                if (i+1 == tab->n_zero) {
                        GBR_lp_set_obj(lp, B->row[1+i+1]+1, dim);
                        ctx->stats->gbr_solved_lps++;
                        unbounded = GBR_lp_solve(lp);
                        isl_assert(ctx, !unbounded, goto error);
                        GBR_lp_get_obj_val(lp, &F_new);
                        fixed = GBR_lp_is_fixed(lp);
                        GBR_set_ui(alpha, 0);
                } else
                if (use_saved) {
                        row = GBR_lp_next_row(lp);
                        GBR_set(F_new, F_saved);
                        fixed = fixed_saved;
                        GBR_set(alpha, alpha_saved[i]);
                } else {
                        row = GBR_lp_add_row(lp, B->row[1+i]+1, dim);
                        GBR_lp_set_obj(lp, B->row[1+i+1]+1, dim);
                        ctx->stats->gbr_solved_lps++;
                        unbounded = GBR_lp_solve(lp);
                        isl_assert(ctx, !unbounded, goto error);
                        GBR_lp_get_obj_val(lp, &F_new);
                        fixed = GBR_lp_is_fixed(lp);

                        GBR_lp_get_alpha(lp, row, &alpha);

                        if (i > 0)
                                save_alpha(lp, row-i, i, alpha_saved);

                        if (GBR_lp_del_row(lp) < 0)
                                goto error;
                }
                GBR_set(F[i+1], F_new);

                GBR_floor(mu[0], alpha);
                GBR_ceil(mu[1], alpha);

                if (isl_int_eq(mu[0], mu[1]))
                        isl_int_set(tmp, mu[0]);
                else {
                        int j;

                        for (j = 0; j <= 1; ++j) {
                                isl_int_set(tmp, mu[j]);
                                isl_seq_combine(b_tmp->el,
                                                ctx->one, B->row[1+i+1]+1,
                                                tmp, B->row[1+i]+1, dim);
                                GBR_lp_set_obj(lp, b_tmp->el, dim);
                                ctx->stats->gbr_solved_lps++;
                                unbounded = GBR_lp_solve(lp);
                                isl_assert(ctx, !unbounded, goto error);
                                GBR_lp_get_obj_val(lp, &mu_F[j]);
                                mu_fixed[j] = GBR_lp_is_fixed(lp);
                                if (i > 0)
                                        save_alpha(lp, row-i, i, alpha_buffer[j]);
                        }

                        if (GBR_lt(mu_F[0], mu_F[1]))
                                j = 0;
                        else
                                j = 1;

                        isl_int_set(tmp, mu[j]);
                        GBR_set(F_new, mu_F[j]);
                        fixed = mu_fixed[j];
                        alpha_saved = alpha_buffer[j];
                }
                isl_seq_combine(B->row[1+i+1]+1, ctx->one, B->row[1+i+1]+1,
                                tmp, B->row[1+i]+1, dim);

                if (i+1 == tab->n_zero && fixed) {
                        if (!GBR_is_zero(F[i+1])) {
                                empty = GBR_lp_cut(lp, B->row[1+i+1]+1);
                                if (empty)
                                        goto done;
                                GBR_set_ui(F[i+1], 0);
                        }
                        tab->n_zero++;
                }

                GBR_set(F_old, F[i]);

                use_saved = 0;
                /* mu_F[0] = 4 * F_new; mu_F[1] = 3 * F_old */
                GBR_set_ui(mu_F[0], 4);
                GBR_mul(mu_F[0], mu_F[0], F_new);
                GBR_set_ui(mu_F[1], 3);
                GBR_mul(mu_F[1], mu_F[1], F_old);
                if (GBR_lt(mu_F[0], mu_F[1])) {
                        B = isl_mat_swap_rows(B, 1 + i, 1 + i + 1);
                        if (i > tab->n_zero) {
                                use_saved = 1;
                                GBR_set(F_saved, F_new);
                                fixed_saved = fixed;
                                if (GBR_lp_del_row(lp) < 0)
                                        goto error;
                                --i;
                        } else {
                                GBR_set(F[tab->n_zero], F_new);
                                if (gbr_only_first && GBR_lt(F[tab->n_zero], two))
                                        break;

                                if (fixed) {
                                        if (!GBR_is_zero(F[tab->n_zero])) {
                                                empty = GBR_lp_cut(lp, B->row[1+tab->n_zero]+1);
                                                if (empty)
                                                        goto done;
                                                GBR_set_ui(F[tab->n_zero], 0);
                                        }
                                        tab->n_zero++;
                                }
                        }
                } else {
                        GBR_lp_add_row(lp, B->row[1+i]+1, dim);
                        ++i;
                }
        } while (i < n_bounded - 1);

        if (0) {
done:
                if (empty < 0) {
error:
                        isl_mat_free(B);
                        B = NULL;
                }
        }

        GBR_lp_delete(lp);

        if (alpha_buffer[1])
                for (i = 0; i < n_bounded; ++i) {
                        GBR_clear(F[i]);
                        GBR_clear(alpha_buffer[0][i]);
                        GBR_clear(alpha_buffer[1][i]);
                }
        free(F);
        free(alpha_buffer[0]);
        free(alpha_buffer[1]);

        isl_vec_free(b_tmp);

        GBR_clear(alpha);
        GBR_clear(F_old);
        GBR_clear(F_new);
        GBR_clear(F_saved);
        GBR_clear(mu_F[0]);
        GBR_clear(mu_F[1]);
        GBR_clear(two);
        GBR_clear(one);

        isl_int_clear(tmp);
        isl_int_clear(mu[0]);
        isl_int_clear(mu[1]);

        tab->basis = B;

        return tab;
}

/* Compute an affine form of a reduced basis of the given basic
 * non-parametric set, which is assumed to be bounded and not
 * include any integer divisions.
 * The first column and the first row correspond to the constant term.
 *
 * If the input contains any equalities, we first create an initial
 * basis with the equalities first.  Otherwise, we start off with
 * the identity matrix.
 */
struct isl_mat *isl_basic_set_reduced_basis(struct isl_basic_set *bset)
{
        struct isl_mat *basis;
        struct isl_tab *tab;

        if (!bset)
                return NULL;

        if (isl_basic_set_dim(bset, isl_dim_div) != 0)
                isl_die(bset->ctx, isl_error_invalid,
                        "no integer division allowed", return NULL);
        if (isl_basic_set_dim(bset, isl_dim_param) != 0)
                isl_die(bset->ctx, isl_error_invalid,
                        "no parameters allowed", return NULL);

        tab = isl_tab_from_basic_set(bset, 0);
        if (!tab)
                return NULL;

        if (bset->n_eq == 0)
                tab->basis = isl_mat_identity(bset->ctx, 1 + tab->n_var);
        else {
                isl_mat *eq;
                unsigned nvar = isl_basic_set_total_dim(bset);
                eq = isl_mat_sub_alloc6(bset->ctx, bset->eq, 0, bset->n_eq,
                                        1, nvar);
                eq = isl_mat_left_hermite(eq, 0, NULL, &tab->basis);
                tab->basis = isl_mat_lin_to_aff(tab->basis);
                tab->n_zero = bset->n_eq;
                isl_mat_free(eq);
        }
        tab = isl_tab_compute_reduced_basis(tab);
        if (!tab)
                return NULL;

        basis = isl_mat_copy(tab->basis);

        isl_tab_free(tab);

        return basis;
}