org.chocosolver.solver.constraints.nary.sum.PropSumBool Maven / Gradle / Ivy
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/*
* This file is part of choco-solver, http://choco-solver.org/
*
* Copyright (c) 2023, 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.sum;
import org.chocosolver.solver.constraints.Operator;
import org.chocosolver.solver.exception.ContradictionException;
import org.chocosolver.solver.variables.BoolVar;
import org.chocosolver.solver.variables.IntVar;
import org.chocosolver.solver.variables.events.IntEventType;
import static org.chocosolver.solver.constraints.PropagatorPriority.BINARY;
import static org.chocosolver.util.tools.ArrayUtils.concat;
/**
* A propagator for SUM(x_i) = y + b, where x_i are boolean variables
*
* Based on "Bounds Consistency Techniques for Long Linear Constraint"
* W. Harvey and J. Schimpf
*
*
* @author Charles Prud'homme
* @since 18/03/11
*/
public class PropSumBool extends PropSum {
/**
* The resulting variable
*/
protected final IntVar sum;
/**
* Creates a sum propagator: SUM(x_i) Op sum + b, where x_i are boolean variables.
* Coefficients are induced by pos:
* those before pos (included) are equal to 1,
* the other ones are equal to -1.
*
* @param variables list of boolean variables
* @param pos position of the last positive (induced) coefficient
* @param o operator
* @param sum resulting variable
* @param b bound to respect
* @param reactOnFineEvent set to true to react on fine events
*/
protected PropSumBool(BoolVar[] variables, int pos, Operator o, IntVar sum, int b, boolean reactOnFineEvent) {
super(concat(variables, sum), pos, o, b, BINARY, reactOnFineEvent);
this.sum = sum;
}
/**
* Creates a sum propagator: SUM(x_i) Op sum + b, where x_i are boolean variables.
* Coefficients are induced by pos:
* those before pos (included) are equal to 1,
* the other ones are equal to -1.
*
* @param variables list of boolean variables
* @param pos position of the last positive (induced) coefficient
* @param o operator
* @param sum resulting variable
* @param b bound to respect
*/
public PropSumBool(BoolVar[] variables, int pos, Operator o, IntVar sum, int b) {
this(variables, pos, o, sum, b, false);
}
@Override
public int getPropagationConditions(int vIdx) {
switch (o) {
case NQ:
return IntEventType.INSTANTIATE.getMask();
case LE:
if (vIdx == l - 1) {
return IntEventType.upperBoundAndInst();
} else {
return IntEventType.instantiation();
}
case GE:
if (vIdx == l - 1) {
return IntEventType.lowerBoundAndInst();
} else {
return IntEventType.instantiation();
}
default:
return IntEventType.boundAndInst();
}
}
@Override
protected void prepare() {
int i = 0, k;
int lb = 0, ub = 0;
for (; i < pos; i++) { // first the positive coefficients
if (vars[i].isInstantiated()) {
k = vars[i].getLB();
lb += k;
ub += k;
} else {
ub++;
}
}
for (; i < l - 1; i++) { // then the negative ones
if (vars[i].isInstantiated()) {
k = vars[i].getLB();
lb -= k;
ub -= k;
} else {
lb--;
}
}
sumLB = lb - sum.getUB();
sumUB = ub - sum.getLB();
}
@Override
protected void filterOnEq() throws ContradictionException {
int F = b - sumLB;
int E = sumUB - b;
if (F < 0 || E < 0) {
fails();
}
int lb, ub, i = 0;
// deal with sum
lb = -sum.getUB();
ub = -sum.getLB();
if (sum.updateLowerBound(-F - lb, this)) {
int nub = -sum.getLB();
E += nub - ub;
ub = nub;
}
if (sum.updateUpperBound(-ub + E, this)) {
int nlb = -sum.getUB();
F -= nlb - lb;
}
if (F <= 0 || E <= 0) { // the main reason we implemented a dedicated version
// positive coefficients first
while (i < pos) {
lb = vars[i].getLB();
if (F <= 0 && vars[i].updateUpperBound(F + lb, this)) {
E++;
}
ub = vars[i].getUB();
if (E <= 0 && vars[i].updateLowerBound(ub - E, this)) {
F++;
}
i++;
}
// then negative ones
while (i < l - 1) {
lb = vars[i].getUB();
if (F <= 0 && vars[i].updateLowerBound(-F + lb, this)) {
E--;
}
ub = vars[i].getLB();
if (E <= 0 && vars[i].updateUpperBound(ub + E, this)) {
F--;
}
i++;
}
}
}
@Override
protected void filterOnLeq() throws ContradictionException {
int F = b - sumLB;
int E = sumUB - b;
if (F < 0) {
fails();
}
int lb, ub, i = 0;
// deal with sum
lb = -sum.getUB();
ub = -sum.getLB();
if (sum.updateLowerBound(-F - lb, this)) {
int nub = -sum.getLB();
E += nub - ub;
}
if (F <= 0) { // the main reason we implemented a dedicated version
// positive coefficients first
while (i < pos) {
lb = vars[i].getLB();
if (vars[i].updateUpperBound(F + lb, this)) {
E++;
}
i++;
}
// then negative ones
while (i < l - 1) {
lb = vars[i].getUB();
if (vars[i].updateLowerBound(-F + lb, this)) {
E--;
}
i++;
}
}
if (E <= 0) {
this.setPassive();
}
}
@Override
protected void filterOnGeq() throws ContradictionException {
int F = b - sumLB;
int E = sumUB - b;
if (E < 0) {
fails();
}
int lb, ub, i = 0;
// deal with sum
lb = -sum.getUB();
ub = -sum.getLB();
if (sum.updateUpperBound(-ub + E, this)) {
int nlb = -sum.getUB();
F -= nlb - lb;
}
if (E <= 0) { // the main reason we implemented a dedicated version
// positive coefficients first
while (i < pos) {
ub = vars[i].getUB();
if (vars[i].updateLowerBound(ub - E, this)) {
F++;
}
i++;
}
// then negative ones
while (i < l - 1) {
ub = vars[i].getLB();
if (vars[i].updateUpperBound(ub + E, this)) {
F--;
}
i++;
}
}
if (F <= 0) {
this.setPassive();
}
}
@Override
public String toString() {
StringBuilder linComb = new StringBuilder(20);
linComb.append(pos == 0 ? "-" : "").append(vars[0].getName());
int i = 1;
for (; i < pos; i++) {
linComb.append(" + ").append(vars[i].getName());
}
for (; i < l - 1; i++) {
linComb.append(" - ").append(vars[i].getName());
}
linComb.append(" ").append(o).append(" ");
linComb.append(vars[i].getName()).append(" ").append(b < 0 ? "- " : "+ ").append(Math.abs(b));
return linComb.toString();
}
@Override
protected PropSum opposite() {
BoolVar[] bvars = new BoolVar[vars.length - 1];
//noinspection SuspiciousSystemArraycopy
System.arraycopy(vars, 0, bvars, 0, bvars.length);
return new PropSumBool(bvars, pos, nop(o), vars[vars.length - 1], b + nb(o), reactToFineEvt);
}
}