AlgoErlangDF.java

/* 
GeoGebra - Dynamic Mathematics for Everyone
http://www.geogebra.org

This file is part of GeoGebra.

This program is free software; you can redistribute it and/or modify it 
under the terms of the GNU General Public License as published by 
the Free Software Foundation.

 */

/*
 * Area of polygon P[0], ..., P[n]
 *
 */

package org.geogebra.common.kernel.statistics;

import org.geogebra.common.kernel.Construction;
import org.geogebra.common.kernel.algos.AlgoElement;
import org.geogebra.common.kernel.arithmetic.BooleanValue;
import org.geogebra.common.kernel.arithmetic.ExpressionNode;
import org.geogebra.common.kernel.arithmetic.FunctionVariable;
import org.geogebra.common.kernel.commands.Commands;
import org.geogebra.common.kernel.geos.GeoElement;
import org.geogebra.common.kernel.geos.GeoFunction;
import org.geogebra.common.kernel.geos.GeoNumberValue;

/**
 * algorithm for FDistribution[0,1,x]
 * 
 * @author Michael
 */
public class AlgoErlangDF extends AlgoElement {

	private GeoNumberValue k, l; // input
	private BooleanValue cumulative; // optional input
	private GeoFunction ret; // output

	@SuppressWarnings("javadoc")
	public AlgoErlangDF(Construction cons, String label, GeoNumberValue mean,
			GeoNumberValue sd, BooleanValue cumulative) {
		this(cons, mean, sd, cumulative);
		ret.setLabel(label);
	}

	@SuppressWarnings("javadoc")
	public AlgoErlangDF(Construction cons, GeoNumberValue a, GeoNumberValue b,
			BooleanValue cumulative) {
		super(cons);
		this.k = a;
		this.l = b;
		this.cumulative = cumulative;
		ret = DistributionFunctionFactory.zeroWhenNegative(cons);

		setInputOutput(); // for AlgoElement

		// compute angle
		compute();
	}

	@Override
	public Commands getClassName() {
		return Commands.Erlang;
	}

	// for AlgoElement
	@Override
	protected void setInputOutput() {

		// dummy function for the "x" argument, eg
		// Normal[0,1,x]
		// Normal[0,1,x,true]
		FunctionVariable fv = new FunctionVariable(kernel);
		GeoFunction dummyFun = fv.wrap().buildFunction(fv);

		input = new GeoElement[cumulative == null ? 3 : 4];
		input[0] = k.toGeoElement();
		input[1] = l.toGeoElement();
		input[2] = dummyFun;
		if (cumulative != null) {
			input[3] = (GeoElement) cumulative;
		}

		super.setOutputLength(1);
		super.setOutput(0, ret);
		setDependencies(); // done by AlgoElement
	}

	/**
	 * @return Normal PDF or CDF function
	 */
	public GeoFunction getResult() {
		return ret;
	}

	@Override
	public void compute() {
		FunctionVariable fv = ret.getFunctionVariables()[0];
		ExpressionNode fvEn = new ExpressionNode(kernel, fv);
		ExpressionNode kEn = new ExpressionNode(kernel, k);
		ExpressionNode lEn = new ExpressionNode(kernel, l);

		ExpressionNode en;

		if (cumulative != null && cumulative.getBoolean()) {

			en = kEn.gammaIncomplete(fvEn.multiply(lEn))
					.divide(kEn.subtract(1).factorial());

			// old hack:
			// command = "If[x<0,0,gamma("+k+",("+l+")x)/("+k+"-1)!]";

		} else {

			en = lEn.power(k).multiply(fvEn.power(kEn.subtract(1)))
					.multiply(lEn.multiply(fv).reverseSign().exp())
					.divide(kEn.subtract(1).factorial());

			// old hack:
			// command =
			// "If[x<0,0,(("+l+")^("+k+")x^("+k+"-1)exp(-("+l+")x))/("+k+"-1)!]";
		}

		ret.getFunctionExpression().setRight(en);

	}

}