z3/src/opt/sortmax.cpp

/*++
Copyright (c) 2014 Microsoft Corporation

Module Name:

    sortmax.cpp

Abstract:

    Theory based MaxSAT.

Author:

    Nikolaj Bjorner (nbjorner) 2016-11-18

Notes:

--*/
#include "opt/maxsmt.h"
#include "util/uint_set.h"
#include "ast/ast_pp.h"
#include "model/model_smt2_pp.h"
#include "smt/smt_theory.h"
#include "smt/smt_context.h"
#include "opt/opt_context.h"
#include "util/sorting_network.h"
#include "ast/converters/generic_model_converter.h"

namespace opt {

    class sortmax : public maxsmt_solver_base {
    public:
        typedef expr* pliteral;
        typedef ptr_vector<expr> pliteral_vector;
        psort_nw<sortmax> m_sort;
        expr_ref_vector   m_trail;
        func_decl_ref_vector m_fresh;
        ref<generic_model_converter> m_filter;
        sortmax(maxsat_context& c, vector<soft>& s, unsigned index): 
            maxsmt_solver_base(c, s, index), m_sort(*this), m_trail(m), m_fresh(m) {}

        lbool operator()() override {
            if (!init()) 
                return l_undef;

            lbool is_sat = l_true;
            m_filter = alloc(generic_model_converter, m, "sortmax");
            expr_ref_vector in(m);
            expr_ref tmp(m);
            ptr_vector<expr> out;
            for (auto const & [e, w, t] : m_soft) {
                if (!w.is_unsigned()) {
                    throw default_exception("sortmax can only handle unsigned weights. Use a different heuristic.");
                }
                unsigned n = w.get_unsigned();
                while (n > 0) {
                    in.push_back(e);
                    --n;
                }
            }
            m_sort.sorting(in.size(), in.data(), out);

            // initialize sorting network outputs using the initial assignment.
            unsigned first = 0;
            for (auto const & [e, w, t] : m_soft) {
                if (t == l_true) {
                    unsigned n = w.get_unsigned();
                    while (n > 0) {
                        s().assert_expr(out[first]);
                        ++first;
                        --n;
                    }
                }
            }
            while (l_true == is_sat && first < out.size() && m_lower < m_upper) {
                trace_bounds("sortmax");
                s().assert_expr(out[first]);
                is_sat = s().check_sat(0, nullptr);
                TRACE(opt, tout << is_sat << "\n"; s().display(tout); tout << "\n";);
                if (!m.inc()) {
                    is_sat = l_undef;
                }
                if (is_sat == l_true) {
                    ++first;
                    s().get_model(m_model);
                    update_assignment();
                    for (; first < out.size() && is_true(out[first]); ++first) { 
                        s().assert_expr(out[first]);
                    }
                    TRACE(opt, model_smt2_pp(tout, m, *m_model.get(), 0););
                    m_upper = m_lower + rational(out.size() - first);
                    (*m_filter)(m_model);
                }
            }
            if (is_sat == l_false) {
                is_sat = l_true;
                m_lower = m_upper;
            }
            TRACE(opt, tout << "min cost: " << m_upper << "\n";);
            return is_sat;
        }

        void update_assignment() {
            for (soft& s : m_soft) s.set_value(is_true(s.s));
        }

        bool is_true(expr* e) {
            return m_model->is_true(e);
        }

        // definitions used for sorting network
        pliteral mk_false() { return m.mk_false(); }
        pliteral mk_true() { return m.mk_true(); }
        pliteral mk_max(unsigned n, pliteral const* as) { return trail(m.mk_or(n, as)); }
        pliteral mk_min(unsigned n, pliteral const* as) { return trail(m.mk_and(std::span<expr* const>(as, n))); }
        pliteral mk_not(pliteral a) { if (m.is_not(a,a)) return a; return trail(m.mk_not(a)); }

        std::ostream& pp(std::ostream& out, pliteral lit) {  return out << mk_pp(lit, m);  }
        
        pliteral trail(pliteral l) {
            m_trail.push_back(l);
            return l;
        }
        pliteral fresh(char const* n) {
            expr_ref fr(m.mk_fresh_const(n, m.mk_bool_sort()), m);
            func_decl* f = to_app(fr)->get_decl();
            m_fresh.push_back(f);
            m_filter->hide(f);
            return trail(fr);
        }
        
        void mk_clause(unsigned n, pliteral const* lits) {
            s().assert_expr(mk_or(m, n, lits));
        }        
        
    };
    
    
    maxsmt_solver_base* mk_sortmax(maxsat_context& c, vector<soft>& s, unsigned index) {
        return alloc(sortmax, c, s, index);
    }

}