| career | drupal | java | mac | mysql | perl | scala | uml | unix  

Groovy example source code file (

This example Groovy source code file ( is included in the "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Groovy tags/keywords

a, a, approximate, atav, atv, atv, av, av, decimalformat, multiplyatav, multiplyatav, multiplyatv, multiplyav, numberformat, text

The Groovy source code

 The Great Computer Language Shootout
 contributed by Java novice Jarkko Miettinen
 modified ~3 lines of the original C#-version 
 by Isaac Gouy
import java.text.DecimalFormat;
import java.text.NumberFormat; 

public class spectralnorm
	private static final NumberFormat formatter = new DecimalFormat("#.000000000");
	public static void main(String[] args) {
		int n = 100;
		if (args.length > 0) n = Integer.parseInt(args[0]);
		System.out.println(formatter.format(new spectralnorm().Approximate(n)));
	private final double Approximate(int n) {
		// create unit vector
		double[] u = new double[n];
		for (int i=0; i<n; i++) u[i] =  1;
		// 20 steps of the power method
		double[] v = new double[n];
		for (int i=0; i<n; i++) v[i] = 0;
		for (int i=0; i<10; i++) {
		// B=AtA         A multiplied by A transposed
		// v.Bv /(v.v)   eigenvalue of v
		double vBv = 0, vv = 0;
		for (int i=0; i<n; i++) {
			vBv += u[i]*v[i];
			vv  += v[i]*v[i];
		return Math.sqrt(vBv/vv);
	/* return element i,j of infinite matrix A */
	private final double A(int i, int j){
		return 1.0/((i+j)*(i+j+1)/2 +i+1);
	/* multiply vector v by matrix A */
	private final void MultiplyAv(int n, double[] v, double[] Av){
		for (int i=0; i<n; i++){
			Av[i] = 0;
			for (int j=0; j<n; j++) Av[i] += A(i,j)*v[j];
	/* multiply vector v by matrix A transposed */
	private final void MultiplyAtv(int n, double[] v, double[] Atv){
		for (int i=0;i<n;i++){
			Atv[i] = 0;
			for (int j=0; j<n; j++) Atv[i] += A(j,i)*v[j];
	/* multiply vector v by matrix A and then by matrix A transposed */
	private final void MultiplyAtAv(int n, double[] v, double[] AtAv){
		double[] u = new double[n];

Other Groovy examples (source code examples)

Here is a short list of links related to this Groovy source code file:

... this post is sponsored by my books ...

#1 New Release!

FP Best Seller


new blog posts


Copyright 1998-2021 Alvin Alexander,
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.