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Groovy example source code file (spectralnorm.groovy)

This example Groovy source code file (spectralnorm.groovy) is included in the DevDaily.com "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, atav, atv, atv, av, av, multiplyatav, multiplyatav, multiplyatv, multiplyav

The Groovy spectralnorm.groovy source code

	The Computer Language Shootout

	contributed by Jochen Hinrichsen

def approximate(n) {
    // create unit vector
	def u = [1.0D] * n

    // 20 steps of the power method
	def v = [0.0D] * n

    for (i in 1..10) {

    // B=AtA         A multiplied by A transposed
    // v.Bv /(v.v)   eigenvalue of v
    double vBv = vv = 0.0D
    for (i in 0..<n) {
        vBv += u[i]*v[i]
        vv  += v[i]*v[i]

    return Math.sqrt(vBv/vv)

/* return element i,j of infinite matrix A */
def A(i, j) {
    return (1.0D) / ((i+j)*(i+j+(1.0D))/(2.0D) +i+(1.0D))

/* multiply vector v by matrix A */
def MultiplyAv(n, v, Av){
    for (i in 0..<n) {
        Av[i] = 0.0D
        for (j in 0..<n) Av[i] += A(i,j)*v[j]

/* multiply vector v by matrix A transposed */
def MultiplyAtv(n, v, Atv){
    for (i in 0..<n) {
        Atv[i] = 0.0D
        for (j in 0..<n) Atv[i] += A(j,i)*v[j]

/* multiply vector v by matrix A and then by matrix A transposed */
def MultiplyAtAv(n, v, AtAv){
    double[] u = new double[n]
    MultiplyAv(n, v, u)
    MultiplyAtv(n, u, AtAv)

def n = (args.length == 0 ? 100 : args[0].toInteger())
def nf = java.text.NumberFormat.getInstance()

// EOF

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