add isl_basic_set_max

[isl.git] / isl_ilp.c

/*
 * Copyright 2008-2009 Katholieke Universiteit Leuven
 *
 * Use of this software is governed by the GNU LGPLv2.1 license
 *
 * Written by Sven Verdoolaege, K.U.Leuven, Departement
 * Computerwetenschappen, Celestijnenlaan 200A, B-3001 Leuven, Belgium
 */

#include <isl_ctx_private.h>
#include <isl_map_private.h>
#include <isl/ilp.h>
#include "isl_sample.h"
#include <isl/seq.h>
#include "isl_equalities.h"
#include <isl_aff_private.h>
#include <isl_local_space_private.h>
#include <isl_mat_private.h>

/* Given a basic set "bset", construct a basic set U such that for
 * each element x in U, the whole unit box positioned at x is inside
 * the given basic set.
 * Note that U may not contain all points that satisfy this property.
 *
 * We simply add the sum of all negative coefficients to the constant
 * term.  This ensures that if x satisfies the resulting constraints,
 * then x plus any sum of unit vectors satisfies the original constraints.
 */
static struct isl_basic_set *unit_box_base_points(struct isl_basic_set *bset)
{
        int i, j, k;
        struct isl_basic_set *unit_box = NULL;
        unsigned total;

        if (!bset)
                goto error;

        if (bset->n_eq != 0) {
                unit_box = isl_basic_set_empty_like(bset);
                isl_basic_set_free(bset);
                return unit_box;
        }

        total = isl_basic_set_total_dim(bset);
        unit_box = isl_basic_set_alloc_dim(isl_basic_set_get_dim(bset),
                                        0, 0, bset->n_ineq);

        for (i = 0; i < bset->n_ineq; ++i) {
                k = isl_basic_set_alloc_inequality(unit_box);
                if (k < 0)
                        goto error;
                isl_seq_cpy(unit_box->ineq[k], bset->ineq[i], 1 + total);
                for (j = 0; j < total; ++j) {
                        if (isl_int_is_nonneg(unit_box->ineq[k][1 + j]))
                                continue;
                        isl_int_add(unit_box->ineq[k][0],
                                unit_box->ineq[k][0], unit_box->ineq[k][1 + j]);
                }
        }

        isl_basic_set_free(bset);
        return unit_box;
error:
        isl_basic_set_free(bset);
        isl_basic_set_free(unit_box);
        return NULL;
}

/* Find an integer point in "bset", preferably one that is
 * close to minimizing "f".
 *
 * We first check if we can easily put unit boxes inside bset.
 * If so, we take the best base point of any of the unit boxes we can find
 * and round it up to the nearest integer.
 * If not, we simply pick any integer point in "bset".
 */
static struct isl_vec *initial_solution(struct isl_basic_set *bset, isl_int *f)
{
        enum isl_lp_result res;
        struct isl_basic_set *unit_box;
        struct isl_vec *sol;

        unit_box = unit_box_base_points(isl_basic_set_copy(bset));

        res = isl_basic_set_solve_lp(unit_box, 0, f, bset->ctx->one,
                                        NULL, NULL, &sol);
        if (res == isl_lp_ok) {
                isl_basic_set_free(unit_box);
                return isl_vec_ceil(sol);
        }

        isl_basic_set_free(unit_box);

        return isl_basic_set_sample_vec(isl_basic_set_copy(bset));
}

/* Restrict "bset" to those points with values for f in the interval [l, u].
 */
static struct isl_basic_set *add_bounds(struct isl_basic_set *bset,
        isl_int *f, isl_int l, isl_int u)
{
        int k;
        unsigned total;

        total = isl_basic_set_total_dim(bset);
        bset = isl_basic_set_extend_constraints(bset, 0, 2);

        k = isl_basic_set_alloc_inequality(bset);
        if (k < 0)
                goto error;
        isl_seq_cpy(bset->ineq[k], f, 1 + total);
        isl_int_sub(bset->ineq[k][0], bset->ineq[k][0], l);

        k = isl_basic_set_alloc_inequality(bset);
        if (k < 0)
                goto error;
        isl_seq_neg(bset->ineq[k], f, 1 + total);
        isl_int_add(bset->ineq[k][0], bset->ineq[k][0], u);

        return bset;
error:
        isl_basic_set_free(bset);
        return NULL;
}

/* Find an integer point in "bset" that minimizes f (in any) such that
 * the value of f lies inside the interval [l, u].
 * Return this integer point if it can be found.
 * Otherwise, return sol.
 *
 * We perform a number of steps until l > u.
 * In each step, we look for an integer point with value in either
 * the whole interval [l, u] or half of the interval [l, l+floor(u-l-1/2)].
 * The choice depends on whether we have found an integer point in the
 * previous step.  If so, we look for the next point in half of the remaining
 * interval.
 * If we find a point, the current solution is updated and u is set
 * to its value minus 1.
 * If no point can be found, we update l to the upper bound of the interval
 * we checked (u or l+floor(u-l-1/2)) plus 1.
 */
static struct isl_vec *solve_ilp_search(struct isl_basic_set *bset,
        isl_int *f, isl_int *opt, struct isl_vec *sol, isl_int l, isl_int u)
{
        isl_int tmp;
        int divide = 1;

        isl_int_init(tmp);

        while (isl_int_le(l, u)) {
                struct isl_basic_set *slice;
                struct isl_vec *sample;

                if (!divide)
                        isl_int_set(tmp, u);
                else {
                        isl_int_sub(tmp, u, l);
                        isl_int_fdiv_q_ui(tmp, tmp, 2);
                        isl_int_add(tmp, tmp, l);
                }
                slice = add_bounds(isl_basic_set_copy(bset), f, l, tmp);
                sample = isl_basic_set_sample_vec(slice);
                if (!sample) {
                        isl_vec_free(sol);
                        sol = NULL;
                        break;
                }
                if (sample->size > 0) {
                        isl_vec_free(sol);
                        sol = sample;
                        isl_seq_inner_product(f, sol->el, sol->size, opt);
                        isl_int_sub_ui(u, *opt, 1);
                        divide = 1;
                } else {
                        isl_vec_free(sample);
                        if (!divide)
                                break;
                        isl_int_add_ui(l, tmp, 1);
                        divide = 0;
                }
        }

        isl_int_clear(tmp);

        return sol;
}

/* Find an integer point in "bset" that minimizes f (if any).
 * If sol_p is not NULL then the integer point is returned in *sol_p.
 * The optimal value of f is returned in *opt.
 *
 * The algorithm maintains a currently best solution and an interval [l, u]
 * of values of f for which integer solutions could potentially still be found.
 * The initial value of the best solution so far is any solution.
 * The initial value of l is minimal value of f over the rationals
 * (rounded up to the nearest integer).
 * The initial value of u is the value of f at the initial solution minus 1.
 *
 * We then call solve_ilp_search to perform a binary search on the interval.
 */
static enum isl_lp_result solve_ilp(struct isl_basic_set *bset,
                                      isl_int *f, isl_int *opt,
                                      struct isl_vec **sol_p)
{
        enum isl_lp_result res;
        isl_int l, u;
        struct isl_vec *sol;

        res = isl_basic_set_solve_lp(bset, 0, f, bset->ctx->one,
                                        opt, NULL, &sol);
        if (res == isl_lp_ok && isl_int_is_one(sol->el[0])) {
                if (sol_p)
                        *sol_p = sol;
                else
                        isl_vec_free(sol);
                return isl_lp_ok;
        }
        isl_vec_free(sol);
        if (res == isl_lp_error || res == isl_lp_empty)
                return res;

        sol = initial_solution(bset, f);
        if (!sol)
                return isl_lp_error;
        if (sol->size == 0) {
                isl_vec_free(sol);
                return isl_lp_empty;
        }
        if (res == isl_lp_unbounded) {
                isl_vec_free(sol);
                return isl_lp_unbounded;
        }

        isl_int_init(l);
        isl_int_init(u);

        isl_int_set(l, *opt);

        isl_seq_inner_product(f, sol->el, sol->size, opt);
        isl_int_sub_ui(u, *opt, 1);

        sol = solve_ilp_search(bset, f, opt, sol, l, u);
        if (!sol)
                res = isl_lp_error;

        isl_int_clear(l);
        isl_int_clear(u);

        if (sol_p)
                *sol_p = sol;
        else
                isl_vec_free(sol);

        return res;
}

static enum isl_lp_result solve_ilp_with_eq(struct isl_basic_set *bset, int max,
                                      isl_int *f, isl_int *opt,
                                      struct isl_vec **sol_p)
{
        unsigned dim;
        enum isl_lp_result res;
        struct isl_mat *T = NULL;
        struct isl_vec *v;

        bset = isl_basic_set_copy(bset);
        dim = isl_basic_set_total_dim(bset);
        v = isl_vec_alloc(bset->ctx, 1 + dim);
        if (!v)
                goto error;
        isl_seq_cpy(v->el, f, 1 + dim);
        bset = isl_basic_set_remove_equalities(bset, &T, NULL);
        v = isl_vec_mat_product(v, isl_mat_copy(T));
        if (!v)
                goto error;
        res = isl_basic_set_solve_ilp(bset, max, v->el, opt, sol_p);
        isl_vec_free(v);
        if (res == isl_lp_ok && sol_p) {
                *sol_p = isl_mat_vec_product(T, *sol_p);
                if (!*sol_p)
                        res = isl_lp_error;
        } else
                isl_mat_free(T);
        isl_basic_set_free(bset);
        return res;
error:
        isl_mat_free(T);
        isl_basic_set_free(bset);
        return isl_lp_error;
}

/* Find an integer point in "bset" that minimizes (or maximizes if max is set)
 * f (if any).
 * If sol_p is not NULL then the integer point is returned in *sol_p.
 * The optimal value of f is returned in *opt.
 *
 * If there is any equality among the points in "bset", then we first
 * project it out.  Otherwise, we continue with solve_ilp above.
 */
enum isl_lp_result isl_basic_set_solve_ilp(struct isl_basic_set *bset, int max,
                                      isl_int *f, isl_int *opt,
                                      struct isl_vec **sol_p)
{
        unsigned dim;
        enum isl_lp_result res;

        if (!bset)
                return isl_lp_error;
        if (sol_p)
                *sol_p = NULL;

        isl_assert(bset->ctx, isl_basic_set_n_param(bset) == 0, goto error);

        if (isl_basic_set_plain_is_empty(bset))
                return isl_lp_empty;

        if (bset->n_eq)
                return solve_ilp_with_eq(bset, max, f, opt, sol_p);

        dim = isl_basic_set_total_dim(bset);

        if (max)
                isl_seq_neg(f, f, 1 + dim);

        res = solve_ilp(bset, f, opt, sol_p);

        if (max) {
                isl_seq_neg(f, f, 1 + dim);
                isl_int_neg(*opt, *opt);
        }

        return res;
error:
        isl_basic_set_free(bset);
        return isl_lp_error;
}

static enum isl_lp_result basic_set_opt(__isl_keep isl_basic_set *bset, int max,
        __isl_keep isl_aff *obj, isl_int *opt)
{
        enum isl_lp_result res;

        if (!obj)
                return isl_lp_error;
        bset = isl_basic_set_copy(bset);
        bset = isl_basic_set_underlying_set(bset);
        res = isl_basic_set_solve_ilp(bset, max, obj->v->el + 1, opt, NULL);
        isl_basic_set_free(bset);
        return res;
}

static __isl_give isl_mat *extract_divs(__isl_keep isl_basic_set *bset)
{
        int i;
        isl_ctx *ctx = isl_basic_set_get_ctx(bset);
        isl_mat *div;

        div = isl_mat_alloc(ctx, bset->n_div,
                            1 + 1 + isl_basic_set_total_dim(bset));
        if (!div)
                return NULL;

        for (i = 0; i < bset->n_div; ++i)
                isl_seq_cpy(div->row[i], bset->div[i], div->n_col);

        return div;
}

enum isl_lp_result isl_basic_set_opt(__isl_keep isl_basic_set *bset, int max,
        __isl_keep isl_aff *obj, isl_int *opt)
{
        int *exp1 = NULL;
        int *exp2 = NULL;
        isl_ctx *ctx;
        isl_mat *bset_div = NULL;
        isl_mat *div = NULL;
        enum isl_lp_result res;

        if (!bset || !obj)
                return isl_lp_error;

        ctx = isl_aff_get_ctx(obj);
        if (!isl_dim_equal(bset->dim, obj->ls->dim))
                isl_die(ctx, isl_error_invalid,
                        "spaces don't match", return isl_lp_error);
        if (!isl_int_is_one(obj->v->el[0]))
                isl_die(ctx, isl_error_unsupported,
                        "expecting integer affine expression",
                        return isl_lp_error);

        if (bset->n_div == 0 && obj->ls->div->n_row == 0)
                return basic_set_opt(bset, max, obj, opt);

        bset = isl_basic_set_copy(bset);
        obj = isl_aff_copy(obj);

        bset_div = extract_divs(bset);
        exp1 = isl_alloc_array(ctx, int, bset_div->n_row);
        exp2 = isl_alloc_array(ctx, int, obj->ls->div->n_row);
        if (!bset_div || !exp1 || !exp2)
                goto error;

        div = isl_merge_divs(bset_div, obj->ls->div, exp1, exp2);

        bset = isl_basic_set_expand_divs(bset, isl_mat_copy(div), exp1);
        obj = isl_aff_expand_divs(obj, isl_mat_copy(div), exp2);

        res = basic_set_opt(bset, max, obj, opt);

        isl_mat_free(bset_div);
        isl_mat_free(div);
        free(exp1);
        free(exp2);
        isl_basic_set_free(bset);
        isl_aff_free(obj);

        return res;
error:
        isl_mat_free(div);
        isl_mat_free(bset_div);
        free(exp1);
        free(exp2);
        isl_basic_set_free(bset);
        isl_aff_free(obj);
        return isl_lp_error;
}

/* Compute the minimum (maximum if max is set) of the integer affine
 * expression obj over the points in set and put the result in *opt.
 */
enum isl_lp_result isl_set_opt(__isl_keep isl_set *set, int max,
        __isl_keep isl_aff *obj, isl_int *opt)
{
        int i;
        enum isl_lp_result res;
        int empty = 1;
        isl_int opt_i;

        if (!set || !obj)
                return isl_lp_error;
        if (set->n == 0)
                return isl_lp_empty;

        res = isl_basic_set_opt(set->p[0], max, obj, opt);
        if (res == isl_lp_error || res == isl_lp_unbounded)
                return res;
        if (set->n == 1)
                return res;
        if (res == isl_lp_ok)
                empty = 0;

        isl_int_init(opt_i);
        for (i = 1; i < set->n; ++i) {
                res = isl_basic_set_opt(set->p[i], max, obj, &opt_i);
                if (res == isl_lp_error || res == isl_lp_unbounded) {
                        isl_int_clear(opt_i);
                        return res;
                }
                if (res == isl_lp_ok)
                        empty = 0;
                if (isl_int_gt(opt_i, *opt))
                        isl_int_set(*opt, opt_i);
        }
        isl_int_clear(opt_i);

        return empty ? isl_lp_empty : isl_lp_ok;
}

enum isl_lp_result isl_basic_set_max(__isl_keep isl_basic_set *bset,
        __isl_keep isl_aff *obj, isl_int *opt)
{
        return isl_basic_set_opt(bset, 1, obj, opt);
}

enum isl_lp_result isl_set_max(__isl_keep isl_set *set,
        __isl_keep isl_aff *obj, isl_int *opt)
{
        return isl_set_opt(set, 1, obj, opt);
}