randomexponential.java

一个一元曲线多项式数值演示例子

package numbercruncher.mathutils;

import java.util.*;

/**
 * Utility class that generates exponentially-distributed
 * random values using several algorithms.
 */
public class RandomExponential {
  private float mean;

  /** generator of uniformly-distributed random values */
  private static Random gen = new Random();

  /**
   * Set the mean.
   * @param mean the mean
   */
  public void setParameters(float mean) {
    this.mean = mean;
  }

  /**
   * Compute the next randomn value using the logarithm algorithm.
   * Requires a uniformly-distributed random value in [0, 1).
   */
  public float nextLog() {
    // Generate a non-zero uniformly-distributed random value.
    float u;
    while ( (u = gen.nextFloat()) == 0) {
      ; // try again if 0
    }

    return (float) ( -mean * Math.log(u));
  }

  /**
   * Compute the next randomn value using the von Neumann algorithm.
   * Requires sequences of uniformly-distributed random values
   * in [0, 1).
   */
  public float nextVonNeumann() {
    int n;
    int k = 0;
    float u1;

    // Loop to try sequences of uniformly-distributed
    // random values.
    for (; ; ) {
      n = 1;
      u1 = gen.nextFloat();

      float u = u1;
      float uPrev = Float.NaN;

      // Loop to generate a sequence of ramdom values
      // as long as they are decreasing.
      for (; ; ) {
        uPrev = u;
        u = gen.nextFloat();

        // No longer decreasing?
        if (u > uPrev) {

          // n is even.
          if ( (n & 1) == 0) {
            return u1 + k; // return a random value
          }

          // n is odd.
          else {
            ++k;
            break; // try another sequence
          }
        }

        ++n;
      }
    }
  }
}