org.chocosolver.solver.constraints.nary.sat.PropSat Maven / Gradle / Ivy
Show all versions of choco-solver Show documentation
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2020, IMT Atlantique. All rights reserved.
*
* Licensed under the BSD 4-clause license.
*
* See LICENSE file in the project root for full license information.
*/
package org.chocosolver.solver.constraints.nary.sat;
import gnu.trove.list.TIntList;
import gnu.trove.list.array.TIntArrayList;
import gnu.trove.map.hash.TIntObjectHashMap;
import gnu.trove.map.hash.TObjectIntHashMap;
import org.chocosolver.memory.IStateInt;
import org.chocosolver.sat.SatSolver;
import org.chocosolver.sat.SatSolver.*;
import org.chocosolver.solver.Model;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.BoolVar;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.ESat;
import java.util.ArrayList;
import static org.chocosolver.sat.SatSolver.*;
/**
* A propagator to deal with clauses and interface a {@link SatSolver}.
*
*
* @author Charles Prud'homme
* @since 12/07/13
*/
public class PropSat extends Propagator {
/**
* The SAT solver
*/
private SatSolver sat_;
/**
* Map between BoolVar and its literal
*/
private TObjectIntHashMap indices_;
/**
* For comparison with SAT solver trail, to deal properly with backtrack
*/
private IStateInt sat_trail_;
/**
* List of early deduction literals
*/
private TIntList early_deductions_;
/**
* Local-like parameter, for #why() method only, lazily initialized.
*/
private TIntObjectHashMap> inClauses;
/**
* Store new added variables when {@link #initialized} is false
*/
private ArrayList add_var;
/**
* Indicates if this is initialized or not
*/
private boolean initialized = false;
/**
* Create a (unique) propagator for clauses recording and propagation.
*
* @param model the solver that declares the propagator
*/
public PropSat(Model model) {
// this propagator initially has no variable
super(new BoolVar[]{model.boolVar(true)}, PropagatorPriority.VERY_SLOW, true);// adds solver.ONE to fit to the super constructor
this.vars = new BoolVar[0]; // erase model.ONE from the variable scope
this.indices_ = new TObjectIntHashMap<>(16,.5f, -1);
sat_ = new SatSolver();
early_deductions_ = new TIntArrayList();
sat_trail_ = model.getEnvironment().makeInt();
add_var = new ArrayList<>(16);
}
@Override
public int getPropagationConditions(int vIdx) {
return IntEventType.instantiation();
}
@Override
public void propagate(int evtmask) throws ContradictionException {
initialize();
if (!sat_.ok_) fails();
sat_.cancelUntil(0);
storeEarlyDeductions();
applyEarlyDeductions();
for (int i = 0; i < vars.length; ++i) {
BoolVar var = vars[i];
if (var.isInstantiated()) {
VariableBound(i);
}
}
}
@Override
public void propagate(int idxVarInProp, int mask) throws ContradictionException {
VariableBound(idxVarInProp);
}
@Override
public ESat isEntailed() {
if (isCompletelyInstantiated()) {
int var, val;
boolean sign;
for (int k : sat_.implies_.keys()) {
sign = sign(negated(k));
var = var(k);
val = vars[var].getValue();
if (val == (sign ? 0 : 1)) {
TIntList lits = sat_.implies_.get(k);
for (int l : lits.toArray()) {
sign = sign(l);
var = var(l);
val = vars[var].getValue();
if (val == (sign ? 0 : 1)) {
return ESat.FALSE;
}
}
}
}
boolean OK = clauseEntailed(sat_.clauses);
OK &= clauseEntailed(sat_.learnts);
return ESat.eval(OK);
}
return ESat.UNDEFINED;
}
/**
* Checks if all clauses from clauses are satisfied
* @param clauses list of clause
* @return true if all clauses are satisfied, false otherwise
*/
private boolean clauseEntailed(ArrayList clauses) {
int lit, var, val;
boolean sign;
for (Clause c : clauses) {
int cnt = 0;
for (int i = 0; i < c.size(); i++) {
lit = c._g(i);
sign = sign(lit);
var = var(lit);
val = vars[var].getValue();
if (val == (sign ? 0 : 1)) cnt++; // if the lit is ok
else break;
}
if (cnt == c.size()) return false;
}
return true;
}
/**
* @return the underlying SAT solver
*/
public SatSolver getSatSolver() {
return sat_;
}
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
* Initializes this propagator
*/
public void initialize() {
if (!initialized) {
if (add_var.size() > 0) {
addVariable(add_var.toArray(new BoolVar[0]));
}
add_var.clear();
this.initialized = true;
}
}
/**
* Creates, or returns if already existing, the literal corresponding to :
*
* expr is true
*
* The negation of the literal is managed outside.
*
* @param expr a boolean variable
* @return its literal
*/
public int makeVar(BoolVar expr) {
int var = indices_.get(expr);
if (var == -1) {
var = sat_.newVariable();
assert (vars.length + add_var.size() == var);
if(initialized) {
addVariable(expr);
}else {
add_var.add(expr);
}
indices_.put(expr, var);
}
return var;
}
/**
* Creates, or returns if already existing, the literal corresponding to :
*
* expr is true
*
* The negation of the literal is managed outside.
*
* @param expr a boolean variable
* @param sign true for even
* @return its literal
*/
public int makeLiteral(BoolVar expr, boolean sign) {
return SatSolver.makeLiteral(makeVar(expr), sign);
}
/**
* The value of the index^th literal is known.
*
* @param index position of the literal
* @throws ContradictionException if inconsistency is detected
*/
private void VariableBound(int index) throws ContradictionException {
try {
if (sat_trail_.get() < sat_.trailMarker()) {
sat_.cancelUntil(sat_trail_.get());
assert (sat_trail_.get() == sat_.trailMarker());
}
int var = index;
boolean sign = vars[index].getValue() != 0;
int lit = SatSolver.makeLiteral(var, sign);
boolean fail = !sat_.propagateOneLiteral(lit);
// Remark: explanations require to instantiated variables even if fail is set to true
sat_trail_.set(sat_.trailMarker());
for (int i = 0; i < sat_.touched_variables_.size(); ++i) {
lit = sat_.touched_variables_.get(i);
var = var(lit);
boolean assigned_bool = sign(lit);
vars[var].instantiateTo(assigned_bool ? 1 : 0, this);
}
if (fail) {
// force failure by removing the last value
vars[index].instantiateTo(1 - vars[index].getValue(), this);
}
}finally {
sat_.touched_variables_.resetQuick(); // issue#327
}
}
public void beforeAddingClauses(){
if (sat_trail_.get() < sat_.trailMarker()) {
sat_.cancelUntil(sat_trail_.get());
assert (sat_trail_.get() == sat_.trailMarker());
}
}
public void afterAddingClauses(){
storeEarlyDeductions();
}
/**
* Add a clause to SAT solver
*
* @param lits clause
* @return false if failure is detected
*/
public boolean addClause(TIntList lits) {
boolean result = sat_.addClause(lits);
storeEarlyDeductions();
return result;
}
/**
* Add learnt clause to SAT solver
*
* @param lits clause
*/
public void addLearnt(int... lits) {
sat_.learnClause(lits);
forcePropagationOnBacktrack(); // issue#327
// early deductions of learnt clause may lead to incorrect behavior on backtrack
// since early deduction is not backtrackable.
}
private void storeEarlyDeductions() {
for (int i = 0; i < sat_.touched_variables_.size(); ++i) {
int lit = sat_.touched_variables_.get(i);
early_deductions_.add(lit);
}
sat_.touched_variables_.resetQuick();
}
private void applyEarlyDeductions() throws ContradictionException {
for (int i = 0; i < early_deductions_.size(); ++i) {
int lit = early_deductions_.get(i);
int var = var(lit);
boolean assigned_bool = sign(lit);
// demons_[var.value()].inhibit(solver());
vars[var].instantiateTo(assigned_bool ? 1 : 0, this);
}
}
}