code: ///////////////////////////////////////////////////////////////////////////
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  //                  / /   ____  ____ _(_)____/ | / / ____/               //
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  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  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                           //
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  //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
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  ///////////////////////////////////////////////////////////////////////////
  
  /*
   * MiniSat -- Copyright (c) 2003-2006, Niklas Een, Niklas Sorensson
   * 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 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT
   * OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   */
  
  package org.logicng.solvers.datastructures;
  
  import org.logicng.datastructures.Tristate;
  
  import java.util.Locale;
  
  /**
   * A variable of the SAT solver for MiniSAT-style solvers.
   * @version 2.0.0
   * @since 1.0
   */
  public final class MSVariable {
      private Tristate assignment;
      private int level;
      private MSClause reason;
      private double activity;
      private boolean polarity;
      private boolean decision;
  
      /**
       * Constructs a new variable with a given initial polarity.
       * @param polarity the initial polarity
       */
      public MSVariable(final boolean polarity) {
          this.assignment = Tristate.UNDEF;
          this.level = -1;
          this.reason = null;
          this.activity = 0;
          this.polarity = polarity;
          this.decision = false;
      }
  
      /**
       * Sets the decision level of this variable.
       * @param level the decision level
       */
      public void setLevel(final int level) {
          this.level = level;
      }
  
      /**
       * Returns the decision level of this variable.
       * @return the decision level of this variable
       */
      public int level() {
          return this.level;
      }
  
      /**
       * Sets the reason for this variable.
       * @param reason the reason for this variable
       */
      public void setReason(final MSClause reason) {
          this.reason = reason;
      }
  
      /**
       * Returns the reason for this variable.
       * @return the reason for this variable
       */
      public MSClause reason() {
          return this.reason;
      }
  
      /**
       * Assigns this variable to a given lifted Boolean.
       * @param assignment the lifted Boolean
       */
      public void assign(final Tristate assignment) {
          this.assignment = assignment;
      }
  
      /**
       * Returns the current assignment of this variable.
       * @return the current assignment of this variable
       */
      public Tristate assignment() {
          return this.assignment;
      }
  
      /**
       * Rescales this variable's activity.
       */
      public void rescaleActivity() {
          this.activity *= 1e-100;
      }
  
      /**
       * Increments this variable's activity by a given value
       * @param inc the increment value
       */
      public void incrementActivity(final double inc) {
          this.activity += inc;
      }
  
      /**
       * Returns the activity of this variable.
       * @return the activity of this variable
       */
      public double activity() {
          return this.activity;
      }
  
      /**
       * Sets the polarity of this variable.
       * @param polarity the polarity of this variable
       */
      public void setPolarity(final boolean polarity) {
          this.polarity = polarity;
      }
  
      /**
       * Returns the polarity of this variable.
       * @return the polarity of this variable
       */
      public boolean polarity() {
          return this.polarity;
      }
  
      /**
       * Returns {@code true} if this variable should be used as a decision variable during solving, {@code false}
       * otherwise.
       * @return {@code true} if this variable should be used as a decision variable
       */
      public boolean decision() {
          return this.decision;
      }
  
      /**
       * Sets whether this variable can be used as a decision variable during solving or not.
       * @param decision {@code true} if it can be used as decision variable, {@code false} otherwise
       */
      public void setDecision(final boolean decision) {
          this.decision = decision;
      }
  
      @Override
      public String toString() {
          return String.format(Locale.ENGLISH, "MSVariable{assignment=%s, level=%d, reason=%s, activity=%f, polarity=%s, decision=%s}",
                  this.assignment, this.level, this.reason, this.activity, this.polarity, this.decision);
      }
  }
  