# spectral-norm Go program

## source code

```/* The Computer Language Benchmarks Game
* https://salsa.debian.org/benchmarksgame-team/benchmarksgame/
*
* contributed by chaishushan
* Based on spectral-norm.go by The Go Authors.
*/

package main

import (
"flag"
"fmt"
"math"
"strconv"
)

// var n = flag.Int("n", 2000, "count")
var n = 0

func evalA(i, j int) int { return ((i+j)*(i+j+1)/2 + i + 1) }

type Vec []float64

func (v Vec) Times(u Vec) {
for i := 0; i < len(v); i++ {
v[i] = 0
for j := 0; j < len(u); j++ {
v[i] += u[j] / float64(evalA(i, j))
}
}
}

func (v Vec) TimesTransp(u Vec) {
for i := 0; i < len(v); i++ {
v[i] = 0
for j := 0; j < len(u); j++ {
v[i] += u[j] / float64(evalA(j, i))
}
}
}

func (v Vec) ATimesTransp(u Vec) {
x := make(Vec, len(u))
x.Times(u)
v.TimesTransp(x)
}

func main() {
flag.Parse()
if flag.NArg() > 0 {
n, _ = strconv.Atoi(flag.Arg(0))
}

N := n
u := make(Vec, N)
for i := 0; i < N; i++ {
u[i] = 1
}
v := make(Vec, N)
for i := 0; i < 10; i++ {
v.ATimesTransp(u)
u.ATimesTransp(v)
}
var vBv, vv float64
for i := 0; i < N; i++ {
vBv += u[i] * v[i]
vv += v[i] * v[i]
}
fmt.Printf("%0.9f\n", math.Sqrt(vBv/vv))
}
```

## notes, command-line, and program output

```NOTES:
go version go1.22.3 linux/amd64
GOAMD64=v2

Thu, 23 May 2024 02:39:26 GMT

MAKE:
/opt/src/go1.22.3/go/bin/go build -o spectralnorm.go_run spectralnorm.go

4.27s to complete and log all make actions

COMMAND LINE:
./spectralnorm.go_run 5500

PROGRAM OUTPUT:
1.274224153
```