Groovy example source code file (spectralnorm.groovy)

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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
	http://shootout.alioth.debian.org/

	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) {
        MultiplyAtAv(n,u,v)
        MultiplyAtAv(n,v,u)
    }

    // 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()
nf.setMaximumFractionDigits(9)
nf.setMinimumFractionDigits(9)
nf.setGroupingUsed(false)
println(nf.format(approximate(n)))

// EOF