org.logicng.cardinalityconstraints.CCAMOBimander 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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/*
* PBLib -- Copyright (c) 2012-2013 Peter Steinke
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*
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package org.logicng.cardinalityconstraints;
import org.logicng.collections.LNGVector;
import org.logicng.datastructures.EncodingResult;
import org.logicng.formulas.Literal;
import org.logicng.formulas.Variable;
/**
* Encodes that at most one variable is assigned value true. Uses the bimander encoding due to Hölldobler and Nguyen.
* @version 2.0.0
* @since 1.1
*/
public final class CCAMOBimander implements CCAtMostOne {
private final LNGVector> groups;
private final LNGVector bits;
private final int m;
private EncodingResult result;
private int numberOfBits;
private int twoPowNBits;
private int k;
/**
* Constructs the bimander AMO encoder with a given number of groups.
*/
CCAMOBimander(final int m) {
this.m = m;
this.groups = new LNGVector<>();
this.bits = new LNGVector<>();
}
@Override
public void build(final EncodingResult result, final Variable... vars) {
result.reset();
this.result = result;
this.encodeIntern(new LNGVector<>(vars));
}
/**
* Internal encoding.
* @param vars the variables of the constraint
*/
private void encodeIntern(final LNGVector vars) {
this.initializeGroups(vars);
this.initializeBits();
int grayCode;
int nextGray;
int i = 0;
int index = -1;
for (; i < this.k; i++) {
index++;
grayCode = i ^ (i >> 1);
i++;
nextGray = i ^ (i >> 1);
for (int j = 0; j < this.numberOfBits; j++) {
if ((grayCode & (1 << j)) == (nextGray & (1 << j))) {
handleGrayCode(grayCode, index, j);
}
}
}
for (; i < this.twoPowNBits; i++) {
index++;
grayCode = i ^ (i >> 1);
for (int j = 0; j < this.numberOfBits; j++) {
handleGrayCode(grayCode, index, j);
}
}
}
private void handleGrayCode(final int grayCode, final int index, final int j) {
if ((grayCode & (1 << j)) != 0) {
for (int p = 0; p < this.groups.get(index).size(); ++p) {
this.result.addClause(this.groups.get(index).get(p).negate(), this.bits.get(j));
}
} else {
for (int p = 0; p < this.groups.get(index).size(); ++p) {
this.result.addClause(this.groups.get(index).get(p).negate(), this.bits.get(j).negate());
}
}
}
/**
* Initializes the groups
* @param vars the variables of the constraint
*/
private void initializeGroups(final LNGVector vars) {
final int n = vars.size();
this.groups.clear();
for (int i = 0; i < this.m; i++) {
this.groups.push(new LNGVector<>());
}
int g = (int) Math.ceil((double) n / this.m);
int ig = 0;
for (int i = 0; i < vars.size(); ) {
while (i < g) {
this.groups.get(ig).push(vars.get(i));
i++;
}
ig++;
g = g + (int) Math.ceil((double) (n - i) / (this.m - ig));
}
for (int i = 0; i < this.groups.size(); i++) {
this.encodeNaive(this.groups.get(i));
}
}
/**
* Initializes the bits.
*/
private void initializeBits() {
this.bits.clear();
this.numberOfBits = (int) Math.ceil(Math.log(this.m) / Math.log(2));
this.twoPowNBits = (int) Math.pow(2, this.numberOfBits);
this.k = (this.twoPowNBits - this.m) * 2;
for (int i = 0; i < this.numberOfBits; ++i) {
this.bits.push(this.result.newVariable());
}
}
/**
* Naive encoding of a cardinality constraint.
* @param vars the variables of the constraint
*/
private void encodeNaive(final LNGVector vars) {
if (vars.size() > 1) {
for (int i = 0; i < vars.size(); i++) {
for (int j = i + 1; j < vars.size(); j++) {
this.result.addClause(vars.get(i).negate(), vars.get(j).negate());
}
}
}
}
@Override
public String toString() {
return this.getClass().getSimpleName();
}
}