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JEP is a Java library for parsing and evaluating mathematical expressions.
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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