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JEP is a Java library for parsing and evaluating mathematical expressions. Use groupId org.fudaa to deploy it in maven central

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/* @author rich
 * Created on 18-Nov-2003
 */
package org.lsmp.djep.xjep.function;

import org.nfunk.jep.*;
import org.nfunk.jep.function.*;

/**
 * The trapezium rule for approximation to a definite integral.
 * h * (y0 + yn + 2(y1+y2+...+y_(n-1)) /2
 * where h = (xn-x0)/n, yi = f(xi)
 * Trapezium(x^2,x,0,10,0.5) 
 * finds an approximation for int(x^2) where x runs from 0 to 10 in steps of 
 * h=0.5. 
 * 
 * @author Rich Morris
 * Created on 10-Sept-2004
 */
public class Trapezium extends SumType {

	static Add add = new Add();
	static Multiply mul = new Multiply();
	static Double HALF = new Double(1.0/2);
	static Double THIRD = new Double(1.0/3);
	static Double TWO = new Double(2);
	static Double FOUR = new Double(4);
	
	public Trapezium()
	{
		super("Trapezium");
	}
	public Trapezium(String name) { super(name); }
		
	public Object evaluate(Object elements[]) throws ParseException
	{
		if(elements.length <2)
			throw new ParseException("Trapezium: there should two or more ordinates, its"+elements.length);

		Object ret = mul.mul(HALF,
				add.add(elements[0],
						elements[elements.length-1]));
		for(int i=1;i