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Open-source constraint solver.
/*
* 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.reification;
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.BoolVar;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.util.ESat;
import org.chocosolver.util.objects.setDataStructures.iterable.IntIterableRangeSet;
/**
* A propagator dedicated to express in a compact way: (x < y + c) ⇔ b
*
* @author Charles Prud'homme
* @since 03/05/2016.
*/
public class PropXltYCReif extends Propagator {
int cste;
public PropXltYCReif(IntVar x, IntVar y, int c, BoolVar r) {
super(new IntVar[]{x, y, r}, PropagatorPriority.TERNARY, false);
this.cste = c;
}
@Override
public void propagate(int evtmask) throws ContradictionException {
if (vars[2].getLB() == 1) {
vars[0].updateUpperBound(vars[1].getUB() + cste - 1, this);
vars[1].updateLowerBound(vars[0].getLB() - cste + 1, this);
if (vars[0].getUB() < vars[1].getLB() + cste) {
this.setPassive();
}
} else if (vars[2].getUB() == 0) {
vars[0].updateLowerBound(vars[1].getLB() + cste, this);
vars[1].updateUpperBound(vars[0].getUB() - cste, this);
if (vars[0].getLB() >= vars[1].getUB() + cste) {
setPassive();
}
} else {
if (vars[0].getUB() < vars[1].getLB() + cste) {
vars[2].instantiateTo(1, this);
setPassive();
} else if (vars[0].getLB() >= vars[1].getUB() + cste) {
vars[2].instantiateTo(0, this);
setPassive();
}
}
}
@Override
public ESat isEntailed() {
if(isCompletelyInstantiated()){
if(vars[2].isInstantiatedTo(1)){
return ESat.eval(vars[0].getValue() < vars[1].getValue() + cste);
}else{
return ESat.eval(vars[0].getValue() >= vars[1].getValue() + cste);
}
}
return ESat.UNDEFINED;
}
/**
* @implSpec
*
* Premise: (x < y + c) ⇔ b
*
* 6 cases here (only cases that triggered filtering are reported):
*
* -
*
* (b = [0,1] ∧ x ∈ (-∞, m] ∧ y ∈ [n, +∞) ∧ m < n + c) → b = 1
*
*
* ⇔ (b = 1 ∨ x ∈ [n + c, +∞) ∨ y ∈ (-∞, n - 1])
*
*
* (alt.) (b = 1 ∨ x ∈ [m + 1, +∞) ∨ y ∈ (-∞, m - c])
*
*
* -
*
* (b = [0,1] ∧ x ∈ [m, +∞) ∧ y ∈ (-∞,n] ∧ m ≥ n + c) → b = 0
*
*
* ⇔ (b = 0 ∨ x ∈ (-∞, m - 1] ∨ y ∈ [m - t + 1,+∞))
*
*
* (alt.) (b = 0 ∨ x ∈ (-∞,n + c - 1] ∨ y ∈ [n + 1, +∞))
*
*
* -
*
* (b = 1 ∧ x ∈ [m, +∞) ∧ y ∈ (-∞, +∞)) → y ∈ [m - c + 1, +∞)
*
*
* ⇔ (b = 0 ∨ x ∈ (-∞, m-1] ∨ y ∈ [m - c + 1, +∞))
*
*
* -
*
* (b = 1 ∧ x ∈ (-∞, +∞) ∧ y ∈ (-∞, n]) → x ∈ (-∞, n + c - 1]
*
*
* ⇔ (b = 0 ∨ x ∈ (-∞, n + c - 1] ∨ y ∈ [n + 1, +∞))
*
*
* -
*
* (b = 0 ∧ x ∈ (-∞,m] ∧ y ∈ (-∞, +∞)) → y ∈ (-∞,m - c]
*
*
* ⇔ (b = 1 ∨ x ∈ [m + 1, +∞) ∨ y ∈ (-∞,m - c])
*
*
* -
*
* (b = 0 ∧ x ∈ (-∞, +∞) ∧ y ∈ [n, +∞)) → x ∈ [n + c, +∞)
*
*
* ⇔ (b = 1 ∨ x ∈ [n + c, +∞) ∨ y ∈ (-∞,n - 1])
*
*
*
*
*
*
*/
@Override
public void explain(int p, ExplanationForSignedClause explanation) {
IntVar pivot = explanation.readVar(p);
if (vars[2].isInstantiatedTo(1)) { // b is true and X < Y + c holds
if (pivot == vars[2]) { // b is the pivot, case a. in javadoc
vars[2].intersectLit(1, explanation);
// deal with alternatives
if(explanation.getFront().getValue(vars[0]) > explanation.getFront().getValue(vars[1])){
int n = explanation.readDom(vars[1]).min();
vars[0].unionLit(n+cste, IntIterableRangeSet.MAX, explanation);
vars[1].unionLit(IntIterableRangeSet.MIN, n - 1, explanation);
}else{
int m = explanation.readDom(vars[0]).max();
vars[0].unionLit(m+1, IntIterableRangeSet.MAX, explanation);
vars[1].unionLit(IntIterableRangeSet.MIN, m - cste, explanation);
}
} else if (pivot == vars[0]) { // x is the pivot, case d. in javadoc
vars[2].unionLit(0, explanation);
int n = explanation.readDom(vars[1]).max();
vars[0].intersectLit(IntIterableRangeSet.MIN, n + cste - 1, explanation);
vars[1].unionLit(n + 1, IntIterableRangeSet.MAX, explanation);
} else if (pivot == vars[1]) { // y is the pivot, case c. in javadoc
vars[2].unionLit(0, explanation);
int m = explanation.readDom(vars[0]).min();
vars[0].unionLit(IntIterableRangeSet.MIN, m - 1, explanation);
vars[1].intersectLit(m - cste + 1, IntIterableRangeSet.MAX, explanation);
}
} else if (vars[2].isInstantiatedTo(0)) {
if (pivot == vars[2]) { // b is the pivot, case b. in javadoc
vars[2].intersectLit(0, explanation);
// deal with alternatives
if(explanation.getFront().getValue(vars[0]) > explanation.getFront().getValue(vars[1])){
int n = explanation.readDom(vars[1]).max();
vars[0].unionLit(IntIterableRangeSet.MIN, n + cste - 1, explanation);
vars[1].unionLit(n + 1, IntIterableRangeSet.MAX, explanation);
}else{
int m = explanation.readDom(vars[0]).min();
vars[0].unionLit(IntIterableRangeSet.MIN, m - 1, explanation);
vars[1].unionLit(m - cste + 1, IntIterableRangeSet.MAX, explanation);
}
} else if (pivot == vars[0]) { // x is the pivot, case f. in javadoc
vars[2].unionLit(1, explanation);
int n = explanation.readDom(vars[1]).min();
vars[0].intersectLit(n + cste, IntIterableRangeSet.MAX, explanation);
vars[1].unionLit(IntIterableRangeSet.MIN, n - 1, explanation);
} else if (pivot == vars[1]) { // y is the pivot, case e. in javadoc
vars[2].unionLit(1, explanation);
int m = explanation.readDom(vars[0]).max();
vars[0].unionLit(m + 1, IntIterableRangeSet.MAX, explanation);
vars[1].intersectLit(IntIterableRangeSet.MIN, m - cste, explanation);
}
} else {
throw new UnsupportedOperationException();
}
}
@Override
public String toString() {
return "(" + vars[0].getName() +" < " + vars[1].getName() + " + "+cste+") <=> "+vars[2].getName();
}
}