org.logicng.cardinalityconstraints.CCAMOBinary Maven / Gradle / Ivy
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// The Next Generation Logic Library //
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// Copyright 2015-20xx Christoph Zengler //
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// Licensed under the Apache License, Version 2.0 (the "License"); //
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// http://www.apache.org/licenses/LICENSE-2.0 //
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/*
* PBLib -- Copyright (c) 2012-2013 Peter Steinke
*
* Permission is hereby granted, free of charge, to any person obtaining a
* copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be included
* in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
* OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package org.logicng.cardinalityconstraints;
import org.logicng.datastructures.EncodingResult;
import org.logicng.formulas.Variable;
/**
* Encodes that at most one variable is assigned value true. Uses the binary encoding due to Doggett, Frisch, Peugniez,
* and Nightingale.
* @version 2.0.0
* @since 1.1
*/
public final class CCAMOBinary implements CCAtMostOne {
/**
* Constructs the binary AMO encoder.
*/
CCAMOBinary() {
//intentionally left empty
}
@Override
public void build(final EncodingResult result, final Variable... vars) {
result.reset();
final int numberOfBits = (int) Math.ceil(Math.log(vars.length) / Math.log(2));
final int twoPowNBits = (int) Math.pow(2, numberOfBits);
final int k = (twoPowNBits - vars.length) * 2;
final Variable[] bits = new Variable[numberOfBits];
for (int i = 0; i < numberOfBits; i++) {
bits[i] = result.newVariable();
}
int grayCode;
int nextGray;
int i = 0;
int index = -1;
while (i < k) {
index++;
grayCode = i ^ (i >> 1);
i++;
nextGray = i ^ (i >> 1);
for (int j = 0; j < numberOfBits; ++j) {
if ((grayCode & (1 << j)) == (nextGray & (1 << j))) {
if ((grayCode & (1 << j)) != 0) {
result.addClause(vars[index].negate(), bits[j]);
} else {
result.addClause(vars[index].negate(), bits[j].negate());
}
}
}
i++;
}
while (i < twoPowNBits) {
index++;
grayCode = i ^ (i >> 1);
for (int j = 0; j < numberOfBits; ++j) {
if ((grayCode & (1 << j)) != 0) {
result.addClause(vars[index].negate(), bits[j]);
} else {
result.addClause(vars[index].negate(), bits[j].negate());
}
}
i++;
}
}
@Override
public String toString() {
return this.getClass().getSimpleName();
}
}