LCGPointSet.java

/*
 * Class:        LCGPointSet
 * Description:  point set defined via a linear congruential recurrence
 * Environment:  Java
 * Software:     SSJ 
 * Copyright (C) 2001  Pierre L'Ecuyer and Universite de Montreal
 * Organization: DIRO, Universite de Montreal
 * @author       
 * @since
 *
 *
 * 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.
 *
 */
package umontreal.ssj.hups;
 
import cern.colt.list.*;

public class LCGPointSet extends CycleBasedPointSet {
 
   private int a; // Multiplier.

   public LCGPointSet(int n, int a) {
      this.a = a;
      double invn = 1.0 / (double) n; // 1/n
      DoubleArrayList c; // Array used to store the current cycle.
      long currentState; // The state currently visited.
      int i;
      boolean stateVisited[] = new boolean[n];
      // Indicates which states have been visited so far.
      for (i = 0; i < n; i++)
         stateVisited[i] = false;
      int startState = 0; // First state of the cycle currently considered.
      numPoints = 0;
      while (startState < n) {
         stateVisited[startState] = true;
         c = new DoubleArrayList();
         c.add(startState * invn);
         // We use the fact that a "long" has 64 bits in Java.
         currentState = (startState * (long) a) % (long) n;
         while (currentState != startState) {
            stateVisited[(int) currentState] = true;
            c.add(currentState * invn);
            currentState = (currentState * (long) a) % (long) n;
         }
         addCycle(c);
         for (i = startState + 1; i < n; i++)
            if (stateVisited[i] == false)
               break;
         startState = i;
      }
   }

   public LCGPointSet(int b, int e, int c, int a) {
      this(computeModulus(b, e, c), a);
   }
 
   private static int computeModulus(int b, int e, int c) {
      int n;
      int i;
      if (b == 2)
         n = (1 << e);
      else {
         for (i = 1, n = b; i < e; i++)
            n *= b;
      }
      n += c;
      return n;
   }
 
   public String toString() {
      StringBuffer sb = new StringBuffer("LCGPointSet with multiplier a = ");
      sb.append(a);
      return sb.toString();
   }

   public int geta() {
      return a;
   }
}