net.finmath.rootfinder.RiddersMethod Maven / Gradle / Ivy
Go to download
Show more of this group Show more artifacts with this name
Show all versions of finmath-lib Show documentation
Show all versions of finmath-lib Show documentation
finmath lib is a Mathematical Finance Library in Java.
It provides algorithms and methodologies related to mathematical finance.
/*
* Created on 17.02.2004
*
* (c) Copyright Christian P. Fries, Germany. Contact: [email protected].
*/
package net.finmath.rootfinder;
/**
* This class implements Ridders root finder as a question-and-answer algorithm.
* The method is documented in Numerical Receipts in C.
*
* @author Christian Fries
* @version 1.1
* @date 2008-04-06
*/
public class RiddersMethod implements RootFinder {
// We store the left and right end point of the intervall
private final double[] points = new double[3]; // left, middle, right
private final double[] values = new double[3]; // left, middle, right
/*
* State of solver
*/
private double nextPoint; // Stores the next point to return by getPoint()
private int solverState = 0; // Internal state of the solver - see setValue()
private int numberOfIterations = 0; // Number of numberOfIterations
private double bestPoint;
private double accuracy = Double.MAX_VALUE; // Current accuracy of solution
private boolean isDone = false; // Will be true if machine accuracy has been reached
public static void main(final String[] args) {
// Test
final RiddersMethod search = new RiddersMethod(-1.0, 5.0);
while(search.getAccuracy() > 1E-13 && !search.isDone()) {
final double x = search.getNextPoint();
final double y = x - 0.656;
search.setValue(y);
System.out.println(search.getAccuracy());
}
System.out.println(search.getNumberOfIterations() + " " + search.getBestPoint());
}
/**
* @param leftPoint left point of search interval
* @param rightPoint right point of search interval
*/
public RiddersMethod(final double leftPoint, final double rightPoint) {
super();
points[0] = leftPoint;
points[2] = rightPoint;
points[1] = (points[0] + points[2]) / 2.0;
nextPoint = points[0];
bestPoint = points[1];
accuracy = points[2]-points[0];
}
/**
* @return Best point optained so far
*/
@Override
public double getBestPoint() {
return bestPoint;
}
/**
* @return Next point for which a value should be set using setValue.
*/
@Override
public double getNextPoint() {
return nextPoint;
}
/**
* @param value Value corresponding to point returned by previous getNextPoint call.
*/
@Override
public void setValue(final double value) {
switch(solverState)
{
case 0:
default:
// State 0: We have asked for left point
values[0] = value;
// In next state ask for right point
nextPoint = points[2];
solverState++;
break;
case 1:
// State 1: We have asked for right point
values[2] = value;
// Calculate next point to propose
points[1] = 0.5*(points[0]+points[2]); // Middle point
// In next state ask for middle point
nextPoint = points[1];
solverState++;
break;
case 2:
// State 2: We have asked for middle point
values[1] = value;
final double s = Math.sqrt(values[1]*values[1]-values[0]*values[2]);
if (s == 0.0) {
accuracy = 0.0;
bestPoint = nextPoint;
isDone = true;
}
// Calculate next point to propose
nextPoint = points[1]+(points[1]-points[0])* (values[0] >= values[2] ? 1.0 : -1.0) *values[1]/s; // Updating formula.
solverState++;
break;
case 3:
// State 3: We have asked for an additional point (stored in next point)
if(value == 0.0)
{
accuracy = 0.0;
bestPoint = nextPoint;
isDone = true;
}
if(sign(values[1],value) != values[1]) // Bookkeeping to keep the root bracketed on next iteration. xl=xm;
{
points[0] = points[1];
values[0] = values[1];
points[2] = nextPoint;
values[2] = value;
}
else if(sign(values[0],value) != values[0])
{
points[2] = nextPoint;
values[2] = value;
}
else if (sign(values[2],value) != values[2])
{
points[0] = nextPoint;
values[0] = value;
}
else
{
System.err.println(this.getClass().getName() + ": Error: Never get here.");
isDone = true;
return;
}
points[1] = 0.5*(points[0]+points[2]); // Middle point
// In next state ask for middle point
nextPoint = points[1];
solverState = 2; // Next state is 2
// Savety belt: check if still improve or if we have reached machine accuracy
// if(Math.abs(points[2]-points[0]) >= accuracy) isDone = true;
break;
}
if(!isDone) {
// Update accuracy
accuracy = Math.abs(points[2]-points[0]);
// Update best point
bestPoint = points[1];
}
numberOfIterations++;
}
/**
* @return Returns the numberOfIterations.
*/
@Override
public int getNumberOfIterations() {
return numberOfIterations;
}
/**
* @return Returns the accuracy.
*/
@Override
public double getAccuracy() {
return accuracy;
}
/**
* @return Returns the isDone.
*/
@Override
public boolean isDone() {
return isDone;
}
private static double sign(final double a, final double b)
{
return b>= 0.0 ? (a>=0 ? a : -a) : (a>0 ? -a : a);
}
}