org.logicng.functions.VariableProfileFunction Maven / Gradle / Ivy
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// The Next Generation Logic Library //
// //
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// Copyright 2015-20xx Christoph Zengler //
// //
// Licensed under the Apache License, Version 2.0 (the "License"); //
// you may not use this file except in compliance with the License. //
// You may obtain a copy of the License at //
// //
// http://www.apache.org/licenses/LICENSE-2.0 //
// //
// Unless required by applicable law or agreed to in writing, software //
// distributed under the License is distributed on an "AS IS" BASIS, //
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or //
// implied. See the License for the specific language governing //
// permissions and limitations under the License. //
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package org.logicng.functions;
import static org.logicng.formulas.cache.FunctionCacheEntry.VARPROFILE;
import org.logicng.formulas.FType;
import org.logicng.formulas.Formula;
import org.logicng.formulas.FormulaFunction;
import org.logicng.formulas.Literal;
import org.logicng.formulas.Variable;
import java.util.HashMap;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* A function that computes the variable profile for a given formula, i.e. it counts the number of occurrences for
* each variable.
*
* For this function, the non-caching version is preferred since it usually performs better. The non-caching version
* of this function generates the result mapping only once and fills it recursively whereas the caching version has to
* construct a new mapping for each sub-formula.
* @version 2.3.0
* @since 1.0
*/
public final class VariableProfileFunction implements FormulaFunction> {
private static final VariableProfileFunction INSTANCE = new VariableProfileFunction();
/**
* @deprecated In the next version, the standard constructor will be replaced by a private constructor.
* In order to instantiate an object of this class, use the {@link #get()} method.
*/
@Deprecated
public VariableProfileFunction() {
// Intentionally left empty
}
/**
* Returns the singleton instance of this function.
* @return an instance of this function
*/
public static VariableProfileFunction get() {
return INSTANCE;
}
/**
* The non-caching implementation of the variable profile computation. In this case the result map is only
* constructed once and results are just added to it.
* @param formula the formula
* @return the variable profile
*/
private static Map nonCachingVariableProfile(final Formula formula) {
final SortedMap map = new TreeMap<>();
nonCachingRecursion(formula, map);
return map;
}
/**
* Recursive function for the non-caching variable profile computation.
* @param formula the formula
* @param map the variable profile
*/
private static void nonCachingRecursion(final Formula formula, final Map map) {
if (formula.type() == FType.LITERAL) {
final Literal lit = (Literal) formula;
map.merge(lit.variable(), 1, Integer::sum);
} else if (formula.type() == FType.PBC) {
for (final Literal l : formula.literals()) {
nonCachingRecursion(l.variable(), map);
}
} else {
for (final Formula op : formula) {
nonCachingRecursion(op, map);
}
}
}
/**
* The caching implementation of the variable profile computation. In this case a result map is constructed for
* each sub-formula.
* @param formula the formula
* @return the variable profile
*/
@SuppressWarnings("unchecked")
private static Map cachingVariableProfile(final Formula formula) {
final Object cached = formula.functionCacheEntry(VARPROFILE);
if (cached != null) {
return (Map) cached;
}
final Map result = new HashMap<>();
if (formula.type() == FType.LITERAL) {
result.put(((Literal) formula).variable(), 1);
} else if (formula.type() == FType.PBC) {
for (final Literal l : formula.literals()) {
result.put(l.variable(), 1);
}
} else {
for (final Formula op : formula) {
final Map temp = cachingVariableProfile(op);
for (final Map.Entry entry : temp.entrySet()) {
result.merge(entry.getKey(), entry.getValue(), Integer::sum);
}
}
}
formula.setFunctionCacheEntry(VARPROFILE, result);
return result;
}
@Override
public Map apply(final Formula formula, final boolean cache) {
return cache ? cachingVariableProfile(formula) : nonCachingVariableProfile(formula);
}
}