org.chocosolver.solver.constraints.binary.PropGreaterOrEqualX_Y Maven / Gradle / Ivy
/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2022, 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.binary;
import org.chocosolver.solver.constraints.Propagator;
import org.chocosolver.solver.constraints.PropagatorPriority;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.learn.ExplanationForSignedClause;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableRangeSet;
/**
* X >= Y
*
*
*
* @author Charles Prud'homme
* @since 1 oct. 2010
*/
public final class PropGreaterOrEqualX_Y extends Propagator {
private final IntVar x;
private final IntVar y;
@SuppressWarnings({"unchecked"})
public PropGreaterOrEqualX_Y(IntVar[] vars) {
super(vars, PropagatorPriority.BINARY, true);
this.x = vars[0];
this.y = vars[1];
}
@Override
public int getPropagationConditions(int vIdx) {
if (vIdx == 0) {
return IntEventType.combine(IntEventType.INSTANTIATE, IntEventType.DECUPP);
} else {
return IntEventType.combine(IntEventType.INSTANTIATE, IntEventType.INCLOW);
}
}
@Override
public void propagate(int evtmask) throws ContradictionException {
x.updateLowerBound(y.getLB(), this);
y.updateUpperBound(x.getUB(), this);
if (x.getLB() >= y.getUB()) {
this.setPassive();
}
}
@Override
public void propagate(int varIdx, int mask) throws ContradictionException {
if (varIdx == 0) {
y.updateUpperBound(x.getUB(), this);
} else {
x.updateLowerBound(y.getLB(), this);
}
if (x.getLB() >= y.getUB()) {
this.setPassive();
}
}
@Override
public ESat isEntailed() {
if (x.getUB() < y.getLB())
return ESat.FALSE;
else if (x.getLB() >= y.getUB())
return ESat.TRUE;
else
return ESat.UNDEFINED;
}
/**
* @implSpec
* Premise: x ≥ y
* The filtering algorithm states that:
*
* - lb(x) ← lb(y) : x cannot be smaller than the smallest value of y
* - ub(y) ← ub(x) : y cannot be greater than the greatest value of x
*
*
*
* Inference rules:
*
* -
* Let m = lb(y), then
*
( x ∈ [m..+∞) ∨ y ∈ (-∞..m - 1] )
*
* -
* Let n = ub(x), then
*
( x ∈ [n + 1..+∞) ∨ y ∈ (-∞..n] )
*
*
*
*/
@Override
public void explain(int p, ExplanationForSignedClause explanation) {
IntIterableRangeSet set;
int m;
if(explanation.readVar(p) == vars[0]){ // case a. (see javadoc)
m = explanation.readDom(vars[1]).min();
set = explanation.complement(vars[1]);
set.retainBetween(IntIterableRangeSet.MIN, m - 1);
vars[0].intersectLit(m, IntIterableRangeSet.MAX, explanation);
vars[1].unionLit(set, explanation);
}else{ // case b. (see javadoc)
assert explanation.readVar(p) == vars[1];
m = explanation.readDom(vars[0]).max();
set = explanation.complement(vars[0]);
set.retainBetween(m + 1, IntIterableRangeSet.MAX);
vars[0].unionLit(set, explanation);
vars[1].intersectLit(IntIterableRangeSet.MIN, m, explanation);
}
}
@Override
public String toString() {
return "prop(" + vars[0].getName() + ".GEQ." + vars[1].getName() + ")";
}
}