content: /**
   * Copyright (c) 2018-2019 Siemens AG
   * All rights reserved.
   * 
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are met:
   * 
   * 1) Redistributions of source code must retain the above copyright notice, this
   *    list of conditions and the following disclaimer.
   * 
   * 2) Redistributions in binary form must reproduce the above copyright notice,
   *    this list of conditions and the following disclaimer in the documentation
   *    and/or other materials provided with the distribution.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
   * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
   * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
   * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  package at.ac.tuwien.kr.alpha.core.solver.heuristics;
  
  import at.ac.tuwien.kr.alpha.api.config.BinaryNoGoodPropagationEstimationStrategy;
  import at.ac.tuwien.kr.alpha.core.common.Assignment;
  import at.ac.tuwien.kr.alpha.core.solver.ChoiceManager;
  
  import java.util.Random;
  
  /**
   * Non-dependency-driven heuristics like {@link BerkMin}, {@link BerkMinLiteral}, and {@link VSIDS}
   * suffer from the fact that choice points comprise only a small portion of all the literals
   * occurring in nogoods and therefore do not influence activity and sign counters as much as
   * other atoms.
   * <p/>
   * The basic idea of {@link DependencyDrivenVSIDS} is therefore to find <i>dependent</i> atoms that can
   * enrich the information available for a choice point. Intuitively, all atoms occurring in the head or the
   * body of a rule depend on a choice point representing the body of this rule.
   * <p/>
   * In contrast to {@link DependencyDrivenHeuristic} and {@link GeneralizedDependencyDrivenHeuristic},
   * this heuristic is based on ideas from VSIDS instead of BerkMin.
   */
  public class DependencyDrivenVSIDS extends VSIDS {
  
  	public DependencyDrivenVSIDS(Assignment assignment, ChoiceManager choiceManager, int decayPeriod, double decayFactor, Random random, BinaryNoGoodPropagationEstimationStrategy momsStrategy) {
  		super(assignment, choiceManager, new HeapOfActiveChoicePoints(decayPeriod, decayFactor, choiceManager), momsStrategy);
  	}
  
  	public DependencyDrivenVSIDS(Assignment assignment, ChoiceManager choiceManager, Random random, BinaryNoGoodPropagationEstimationStrategy momsStrategy) {
  		this(assignment, choiceManager, DEFAULT_DECAY_PERIOD, DEFAULT_DECAY_FACTOR, random, momsStrategy);
  	}
  	
  	/**
  	 * Returns the head derived by the rule corresponding to the given choice point,
  	 * since the head atom may give more relevant information than the atom representing rule body.
  	 */
  	@Override
  	protected int getAtomForChooseSign(int atom) {
  		Integer head = choiceManager.getHeadDerivedByChoiceAtom(atom);
  		if (head != null) {
  			atom = head;
  		}
  		return atom;
  	}
  
  }
  