1c/benchmark/spectralnorm.ts

// https://benchmarksgame.alioth.debian.org/u64q/program.php?test=spectralnorm&lang=typescript&id=1

function approximate(n: number): number {
    let u = Array(n), v = Array(n)
    for (let i = 0; i < n; ++i) {
        u[i] = 1.0
    }
    for (let i = 0; i < 10; ++i) {
        multiplyAtAv(n, u, v)
        multiplyAtAv(n, v, u)
    }
    let vBv = 0.0, vv = 0.0
    for (let i = 0; i < 10; ++i) {
        vBv += u[i] * v[i]
        vv += v[i] * v[i]
    }
    return Math.sqrt(vBv / vv)
}

function a(i, j: number): number {
    return 1.0 / ((i + j) * ((i + j) + 1) / 2 + i + 1)
}

function multiplyAv(n: number, v: number[], av: number[]) {
    for (let i = 0; i < n - 1; ++i) {
        av[i] = 0.0
        for (let j = 0; j < n - 1; ++j) {
            av[i] += a(i, j) * v[j]
        }
    }
}

function multiplyAtv(n: number, v: number[], atv: number[]) {
    for (let i = 0; i < n - 1; ++i) {
        atv[i] = 0.0
        for (let j = 0; j < n - 1; ++j) {
            atv[i] += a(j, i) * v[j]
        }
    }
}

function multiplyAtAv(n: number, v: number[], atAv: number[]) {
    let u = new Array(n)
    multiplyAv(n, v, u)
    multiplyAtv(n, u, atAv)
}

{
    let start = Date.now()
    echo(approximate(5500).toFixed(9))
    echo(Date.now() - start + "ms")
}