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Open-source constraint solver.
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2019, 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.ternary;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.exception.SolverException;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.ESat;
/**
* X = MIN(Y,Z)
*
* ensures bound consistency
*
* @author Charles Prud'homme
* @since 19/04/11
*/
public class PropMinBC extends Propagator {
private IntVar BST, v1, v2;
public PropMinBC(IntVar X, IntVar Y, IntVar Z) {
super(new IntVar[]{X, Y, Z}, PropagatorPriority.TERNARY, false);
this.BST = vars[0];
this.v1 = vars[1];
this.v2 = vars[2];
}
@Override
public int getPropagationConditions(int vIdx) {
return IntEventType.boundAndInst();
}
@Override
public void propagate(int evtmask) throws ContradictionException {
filter();
}
private void filter() throws ContradictionException {
int c = 0;
c += (vars[0].isInstantiated() ? 1 : 0);
c += (vars[1].isInstantiated() ? 2 : 0);
c += (vars[2].isInstantiated() ? 4 : 0);
switch (c) {
case 7: // everything is instantiated
case 6:// Z and Y are instantiated
vars[0].instantiateTo(Math.min(vars[1].getValue(), vars[2].getValue()), this);
break;
case 5: // X and Z are instantiated
{
int best = vars[0].getValue();
int val2 = vars[2].getValue();
if (best < val2) {
vars[1].instantiateTo(best, this);
} else if (best > val2) {
fails(); // TODO: could be more precise, for explanation purpose
} else { // X = Z
vars[1].updateLowerBound(best, this);
}
}
break;
case 4: // Z is instantiated
{
int val = vars[2].getValue();
if (val < vars[1].getLB()) { // => X = Z
if(vars[0].instantiateTo(val, this)) {
setPassive();
}
} else {
_filter();
}
}
break;
case 3:// X and Y are instantiated
{
int best = vars[0].getValue();
int val1 = vars[1].getValue();
if (best < val1) {
vars[2].instantiateTo(best, this);
} else if (best > val1) {
fails(); // TODO: could be more precise, for explanation purpose
} else { // X = Y
vars[2].updateLowerBound(best, this);
}
}
break;
case 2: // Y is instantiated
{
int val = vars[1].getValue();
if (val < vars[2].getLB()) { // => X = Y
if(vars[0].instantiateTo(val, this)) {
setPassive();
}
} else { // val in Z
_filter();
}
}
break;
case 1: // X is instantiated
{
int best = vars[0].getValue();
if (!vars[1].contains(best) && !vars[2].contains(best)) {
fails(); // TODO: could be more precise, for explanation purpose
}
if (vars[1].getLB() > best) {
if(vars[2].instantiateTo(best, this)) {
setPassive();
}
} else if (vars[2].getLB() > best) {
if(vars[1].instantiateTo(best, this)) {
setPassive();
}
} else {
if (vars[1].updateLowerBound(best, this) | vars[2].updateLowerBound(best, this)) {
filter(); // to ensure idempotency for "free"
}
}
}
break;
case 0: // otherwise
_filter();
break;
default: throw new SolverException("Unexpected mask "+c);
}
}
private void _filter() throws ContradictionException {
boolean change;
do {
change = vars[0].updateLowerBound(Math.min(vars[1].getLB(), vars[2].getLB()), this);
change |= vars[0].updateUpperBound(Math.min(vars[1].getUB(), vars[2].getUB()), this);
change |= vars[1].updateLowerBound(vars[0].getLB(), this);
change |= vars[2].updateLowerBound(vars[0].getLB(), this);
if (vars[2].getLB() > vars[0].getUB()) {
change |= vars[1].updateUpperBound(vars[0].getUB(), this);
}
if (vars[1].getLB() > vars[0].getUB()) {
change |= vars[2].updateUpperBound(vars[0].getUB(), this);
}
} while (change);
}
@Override
public ESat isEntailed() {
int lb = vars[0].getLB();
if (vars[1].getUB() < lb || vars[2].getUB() < lb) {
return ESat.FALSE;
}
if (Math.min(vars[1].getLB(), vars[2].getLB()) > vars[0].getUB()) {
return ESat.FALSE;
}
if (vars[1].getLB() < lb || vars[2].getLB() < lb) {
return ESat.UNDEFINED;
}
if (vars[0].isInstantiated()) {
if (vars[1].isInstantiatedTo(lb) || vars[2].isInstantiatedTo(lb)) {
return ESat.TRUE;
}
}
return ESat.UNDEFINED;
}
@Override
public String toString() {
return BST.toString() + ".MIN(" + v1.toString() + "," + v2.toString() + ")";
}
}