org.chocosolver.solver.constraints.binary.PropGreaterOrEqualX_YC Maven / Gradle / Ivy
/*
* 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.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.learn.Implications;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IntEventType;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.ValueSortedMap;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableRangeSet;
import org.chocosolver.util.tools.MathUtils;
/**
* X >= Y + C
*
*
*
* @author Charles Prud'homme
* @since 13/06/12
*/
public final class PropGreaterOrEqualX_YC extends Propagator {
private final IntVar x;
private final IntVar y;
private final int cste;
@SuppressWarnings({"unchecked"})
public PropGreaterOrEqualX_YC(IntVar[] vars, int c) {
super(vars, PropagatorPriority.BINARY, true);
this.x = vars[0];
this.y = vars[1];
this.cste = c;
}
@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(MathUtils.safeAdd(y.getLB(), this.cste), this);
y.updateUpperBound(MathUtils.safeSubstract(x.getUB(), this.cste), this);
if (x.getLB() >= y.getUB() + this.cste) {
this.setPassive();
}
}
@Override
public void propagate(int idxVarInProp, int mask) throws ContradictionException {
if (idxVarInProp == 0) {
y.updateUpperBound(x.getUB() - this.cste, this);
} else {
x.updateLowerBound(y.getLB() + this.cste, this);
}
if (x.getLB() >= y.getUB() + this.cste) {
this.setPassive();
}
}
@Override
public ESat isEntailed() {
if (x.getUB() < y.getLB() + cste)
return ESat.FALSE;
else if (x.getLB() >= y.getUB() + this.cste)
return ESat.TRUE;
else
return ESat.UNDEFINED;
}
/**
* @implSpec
* Premise: x ≥ y + c
* The filtering algorithm states that:
*
* - lb(x) ← lb(y) + c : x cannot be smaller than the smallest value of y plus c
* - ub(y) ← ub(x) - c : y cannot be greater than the greatest value of x minus c
*
*
*
* Inference rules:
*
* -
* Let m = lb(y), then
*
( x ∈ [m + c..+∞) ∨ y ∈ (-∞..m - 1] )
*
* -
* Let n = ub(x), then
*
( x ∈ [n + 1..+∞) ∨ y ∈ (-∞..n - c] )
*
*
*
*/
@Override
public void explain(ExplanationForSignedClause explanation,
ValueSortedMap front,
Implications ig, int p) {
IntIterableRangeSet set0, set1;
int m;
boolean isPivot;
if (isPivot = (ig.getIntVarAt(p) == vars[0])) { // case a. (see javadoc)
m = explanation.getSet(vars[1]).min();
set0 = explanation.getRootSet(vars[0]);
set1 = explanation.getComplementSet(vars[1]);
set0.retainBetween(m + cste, IntIterableRangeSet.MAX);
set1.retainBetween(IntIterableRangeSet.MIN, m - 1);
} else { // case b. (see javadoc)
assert ig.getIntVarAt(p) == vars[1];
m = explanation.getSet(vars[0]).max();
set0 = explanation.getComplementSet(vars[0]);
set1 = explanation.getRootSet(vars[1]);
set0.retainBetween(m + 1, IntIterableRangeSet.MAX);
set1.retainBetween(IntIterableRangeSet.MIN, m - cste);
}
explanation.addLiteral(vars[0], set0, isPivot);
explanation.addLiteral(vars[1], set1, !isPivot);
}
@Override
public String toString() {
return x.getName() + " >= " + y.getName() + " + " + cste;
}
}