toxgene.core.random.ToxExponential Maven / Gradle / Ivy

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/**
 * Implements a random generator for exponential probability distributions
 *
 * @author Denilson Barbosa
 * @version 0.1
 */

package toxgene.core.random;

import java.util.Random;
import toxgene.core.ToXgeneErrorException;
import toxgene.core.genes.CreateGeneException;

public class ToxExponential implements ToxRandom{
  private float min, max, B;
  private double U;
  private Random rand;

  public ToxExponential(float min, float max, float B, long seed){
		this.min = min;
		this.max = max;
		this.B = B;

		if (max < min){
			throw new CreateGeneException("invalid min and max values for "+
																		"ToxExponential random generator!");
		}

		if (B < min || B > max){
			throw new CreateGeneException(" invalid mean value for "+
																		"ToxExponential random generator!");
		}

		rand = new Random(seed);
  }

  public long nextInt(){
		return (Math.round(nextDouble()));
  }

  private double nextDouble(){
		U = 1.0 - rand.nextDouble();
		double temp = -B*Math.log(U);

		if (temp < min)
			return (double) min;

		if (temp > max)
			return (double) max;

		return temp;
  }

  public float nextFloat(){
		float result = (float) nextDouble();

		//check for consistency
		if (result < min)
			result = min;
		if (result > max)
			result = max;

		return result;
  }

  public float minValue(){
		return min;
  }

  public float maxValue(){
		return max;
  }

  public long nextInt(float value){
		//in some cases we call this function with the max_value as parameter :(
		if (value == max)
			return ((long)nextFloat());

		if (value < min){
			throw new ToXgeneErrorException("cannot update distribution max value: "+
																			value+" is smaller than minimum value: "
																			+min);
		}
	
		return (Math.round((double)min + ((value-min)*nextDouble())));
  }
}