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jeremybenn |
/*
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Redistribution and use in source and binary forms, with or without
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modification, are permitted provided that the following conditions are met:
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* Redistributions of source code must retain the above copyright
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notice, this list of conditions and the following disclaimer.
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* Redistributions in binary form must reproduce the above copyright
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notice, this list of conditions and the following disclaimer in the
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documentation and/or other materials provided with the distribution.
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* Neither the name of "The Computer Language Benchmarks Game" nor the
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name of "The Computer Language Shootout Benchmarks" nor the names of
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its contributors may be used to endorse or promote products derived
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from this software without specific prior written permission.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
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LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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POSSIBILITY OF SUCH DAMAGE.
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*/
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/* The Computer Language Benchmarks Game
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* http://shootout.alioth.debian.org/
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*
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* contributed by The Go Authors.
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* Based on spectral-norm.c by Sebastien Loisel
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*/
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package main
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import (
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"flag"
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"fmt"
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"math"
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)
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var n = flag.Int("n", 2000, "count")
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func evalA(i, j int) float64 { return 1 / float64(((i+j)*(i+j+1)/2 + i + 1)) }
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type Vec []float64
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func (v Vec) Times(u Vec) {
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for i := 0; i < len(v); i++ {
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v[i] = 0
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for j := 0; j < len(u); j++ {
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v[i] += evalA(i, j) * u[j]
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}
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}
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}
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func (v Vec) TimesTransp(u Vec) {
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for i := 0; i < len(v); i++ {
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v[i] = 0
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for j := 0; j < len(u); j++ {
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v[i] += evalA(j, i) * u[j]
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}
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}
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}
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func (v Vec) ATimesTransp(u Vec) {
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x := make(Vec, len(u))
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x.Times(u)
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v.TimesTransp(x)
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}
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func main() {
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flag.Parse()
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N := *n
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u := make(Vec, N)
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for i := 0; i < N; i++ {
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u[i] = 1
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}
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v := make(Vec, N)
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for i := 0; i < 10; i++ {
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v.ATimesTransp(u)
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u.ATimesTransp(v)
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}
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var vBv, vv float64
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for i := 0; i < N; i++ {
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vBv += u[i] * v[i]
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vv += v[i] * v[i]
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}
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fmt.Printf("%0.9f\n", math.Sqrt(vBv/vv))
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}
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