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/*++
Copyright (c) 2020 Microsoft Corporation
Module Name:
int_cube.h
Abstract:
Cube finder
This routine attempts to find a feasible integer solution
by tightnening bounds and running an LRA solver on the
tighter system.
find_largest_cube() implements the largest cube test of
Bromberger and Weidenbach (Fast Cube Tests for LIA Constraint
Solving, IJCAR 2016): a fresh variable x_e for the cube edge
length is introduced and maximized; the center of the largest
cube is rounded to a candidate integer solution.
Author:
Nikolaj Bjorner (nbjorner)
Lev Nachmanson (levnach)
Revision History:
--*/
#pragma once
#include "util/vector.h"
#include "math/lp/lia_move.h"
#include "math/lp/numeric_pair.h"
#include "math/lp/lar_term.h"
namespace lp {
class int_solver;
class lar_solver;
class int_cube {
class int_solver& lia;
class lar_solver& lra;
// a fractional integer coordinate of the cube center:
// the candidate value is m_lo or m_lo + 1
struct flip_candidate {
unsigned m_j = 0;
mpq m_lo;
bool m_at_hi = false;
};
// a term column with at least one bound, tracked during the repair
struct bounded_row {
unsigned m_j = 0;
impq m_val;
};
bool tighten_term_for_cube(unsigned i);
bool tighten_terms_for_cube();
void find_feasible_solution();
impq get_cube_delta_for_term(const lar_term& t) const;
bool add_edge_rows_for_term(unsigned i, unsigned x_e);
bool add_cube_edge_rows(unsigned x_e);
lia_move sat_after_rounding();
lia_move round_and_repair();
bool repair_rounded_candidate(vector<flip_candidate>& flips);
public:
int_cube(int_solver& lia);
lia_move operator()();
lia_move find_largest_cube();
};
}