Initial project import

tools/v/examples/spectral.v

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+/*
+https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/spectralnorm.html
+Added: Pradeep Verghese
+Benchmarks:
+Used v -prod spectral.v
+Command: time ./spectral 5500
+Output: 1.274224153
+
+Time: 11.67s user 0.02s system 99% cpu 11.721 total
+*/
+module main
+
+import math
+import os
+import strconv
+
+fn evala(i int, j int) int {
+	return (i + j) * (i + j + 1) / 2 + i + 1
+}
+
+fn times(mut v []f64, u []f64) {
+	for i in 0 .. v.len {
+		mut a := f64(0)
+		for j in 0 .. u.len {
+			a += u[j] / f64(evala(i, j))
+		}
+		v[i] = a
+	}
+}
+
+fn times_trans(mut v []f64, u []f64) {
+	for i in 0 .. v.len {
+		mut a := f64(0)
+		for j in 0 .. u.len {
+			a += u[j] / f64(evala(j, i))
+		}
+		v[i] = a
+	}
+}
+
+fn a_times_transp(mut v []f64, u []f64) {
+	mut x := []f64{len: u.len, init: 0}
+	times(mut x, u)
+	times_trans(mut v, x)
+}
+
+fn main() {
+	mut n := 0
+	if os.args.len == 2 {
+		n = strconv.atoi(os.args[1]) or { 0 }
+	} else {
+		n = 0
+	}
+	mut u := []f64{len: n, init: 1}
+	mut v := []f64{len: n, init: 1}
+	for _ in 0 .. 10 {
+		a_times_transp(mut v, u)
+		a_times_transp(mut u, v)
+	}
+	mut vbv := f64(0)
+	mut vv := f64(0)
+	for i in 0 .. n {
+		vbv += u[i] * v[i]
+		vv += v[i] * v[i]
+	}
+	ans := math.sqrt(vbv / vv)
+	println('${ans:0.9f}')
+}