PoissonIntegerGenerator.java

/* Copyright (c) 2009 Miltiadis Allamanis
 * 
 * The MIT License
 * 
 * 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 app.randgen.backend;

import android.app.Activity;
import android.widget.EditText;
import android.widget.Toast;

/**
 * A RandomGenerator that produces integers following the Poisson distribution
 */
public class PoissonIntegerGenerator extends RandomGenerator {
	/* {author=Miltiadis Allamanis} */

	public double lambda;
	private boolean parametrized = false;

	@Override
	public String getDescription() {
		return "Creates random numbers following the Poisson distribution";
	}

	@Override
	public String getName() {
		return "Poisson Distribution";
	}

	@Override
	public String getNext() {
		if (!parametrized)
			return "Parameters not set";

		// Knuth's method
		double L = Math.exp(-lambda);
		double p = 1;
		int k = 0;
		do {
			k++;
			p *= generator.nextDouble();
		} while (p >= L);

		return Integer.toString(k - 1);
	}

	@Override
	public int getParamsLayoutID() {
		return app.randgen.R.id.poissonParams;
	}

	@Override
	public boolean setParameters(final Activity myActivity) {
		try {
			EditText edit = (EditText) myActivity
					.findViewById(app.randgen.R.id.poissonMean);
			lambda = Double.parseDouble(edit.getText().toString());
			parametrized = true;
			return true;
		} catch (Exception e) {
			Toast error = Toast.makeText(myActivity,
					app.randgen.R.string.paramError, Toast.LENGTH_SHORT);
			error.show();
			return false;
		}
	}
}