randomexponential.java~1~

来自「一个一元曲线多项式数值演示例子」· JAVA~1~ 代码 · 共 80 行

package numbercruncher.mathutils;

import java.util.Random;

/**
 * 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;
            }
        }
    }
}