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/*
* 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.nary.sum;
import org.chocosolver.memory.IStateInt;
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.PropagatorEventType;
/**
* A propagator for SUM(x_i) = y + b, where x_i are boolean variables, maintained incrementally.
*
* Based on "Bounds Consistency Techniques for Long Linear Constraint"
* W. Harvey and J. Schimpf
*
*
* @author Charles Prud'homme
* @since 18/03/11
*/
public class PropSumBoolIncr extends PropSumBool {
/**
* Sum of lower bounds maintained incrementally.
* Main reason this version exists.
*/
private IStateInt bLB;
/**
* Sum of upper bounds maintained incrementally.
* Main reason this version exists.
*/
private IStateInt bUB;
/**
* The filtering algorithm is triggered on some particular events.
* This boolean indicates when the propagation should be executed.
*
*/
private boolean doFilter;
/**
* Creates a sum propagator: SUM(x_i) Op sum + b, where x_i are boolean variables, maintained incrementally.
* 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 PropSumBoolIncr(BoolVar[] variables, int pos, Operator o, IntVar sum, int b) {
super(variables, pos, o, sum, b, true);
this.bLB = model.getEnvironment().makeInt();
this.bUB = model.getEnvironment().makeInt();
}
@Override
public void propagate(int evtmask) throws ContradictionException {
if (PropagatorEventType.isFullPropagation(evtmask)) {
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--;
}
}
bLB.set(lb);
bUB.set(ub);
}
doFilter = false;
filter();
}
@Override
public void propagate(int idxVarInProp, int mask) throws ContradictionException {
if (idxVarInProp < pos) {
int k = vars[idxVarInProp].getLB();
if (k == 1) {
bLB.add(1);
doFilter |= o != Operator.GE;
} else {
bUB.add(-1);
doFilter |= o != Operator.LE;
}
} else if (idxVarInProp < l -1) {
int k = vars[idxVarInProp].getLB();
if (k == 0) {
bLB.add(1);
doFilter |= o != Operator.GE;
} else {
bUB.add(-1);
doFilter |= o != Operator.LE;
}
} else {
doFilter = true;
}
if (doFilter) {
forcePropagate(PropagatorEventType.CUSTOM_PROPAGATION);
}
}
@Override
protected void prepare() {
sumLB = bLB.get() - sum.getUB();
sumUB = bUB.get() - sum.getLB();
}
@Override
protected PropSum opposite(){
BoolVar[] bvars = new BoolVar[vars.length-1];
//noinspection SuspiciousSystemArraycopy
System.arraycopy(vars, 0, bvars, 0, bvars.length);
return new PropSumBoolIncr(bvars, pos, nop(o), vars[vars.length-1], b + nb(o));
}
}