1/*
2Redistribution and use in source and binary forms, with or without
3modification, are permitted provided that the following conditions are met:
4
5    * Redistributions of source code must retain the above copyright
6    notice, this list of conditions and the following disclaimer.
7
8    * Redistributions in binary form must reproduce the above copyright
9    notice, this list of conditions and the following disclaimer in the
10    documentation and/or other materials provided with the distribution.
11
12    * Neither the name of "The Computer Language Benchmarks Game" nor the
13    name of "The Computer Language Shootout Benchmarks" nor the names of
14    its contributors may be used to endorse or promote products derived
15    from this software without specific prior written permission.
16
17THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
21LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27POSSIBILITY OF SUCH DAMAGE.
28*/
29
30/* The Computer Language Benchmarks Game
31 * http://shootout.alioth.debian.org/
32 *
33 * contributed by The Go Authors.
34 * Based on spectral-norm.c by Sebastien Loisel
35 */
36
37package main
38
39import (
40	"flag"
41	"fmt"
42	"math"
43	"runtime"
44)
45
46var n = flag.Int("n", 2000, "count")
47var nCPU = flag.Int("ncpu", 4, "number of cpus")
48
49func evalA(i, j int) float64 { return 1 / float64(((i+j)*(i+j+1)/2 + i + 1)) }
50
51type Vec []float64
52
53func (v Vec) Times(i, n int, u Vec, c chan int) {
54	for ; i < n; i++ {
55		v[i] = 0
56		for j := 0; j < len(u); j++ {
57			v[i] += evalA(i, j) * u[j]
58		}
59	}
60	c <- 1
61}
62
63func (v Vec) TimesTransp(i, n int, u Vec, c chan int) {
64	for ; i < n; i++ {
65		v[i] = 0
66		for j := 0; j < len(u); j++ {
67			v[i] += evalA(j, i) * u[j]
68		}
69	}
70	c <- 1
71}
72
73func wait(c chan int) {
74	for i := 0; i < *nCPU; i++ {
75		<-c
76	}
77}
78
79func (v Vec) ATimesTransp(u Vec) {
80	x := make(Vec, len(u))
81	c := make(chan int, *nCPU)
82	for i := 0; i < *nCPU; i++ {
83		go x.Times(i*len(v) / *nCPU, (i+1)*len(v) / *nCPU, u, c)
84	}
85	wait(c)
86	for i := 0; i < *nCPU; i++ {
87		go v.TimesTransp(i*len(v) / *nCPU, (i+1)*len(v) / *nCPU, x, c)
88	}
89	wait(c)
90}
91
92func main() {
93	flag.Parse()
94	runtime.GOMAXPROCS(*nCPU)
95	N := *n
96	u := make(Vec, N)
97	for i := 0; i < N; i++ {
98		u[i] = 1
99	}
100	v := make(Vec, N)
101	for i := 0; i < 10; i++ {
102		v.ATimesTransp(u)
103		u.ATimesTransp(v)
104	}
105	var vBv, vv float64
106	for i := 0; i < N; i++ {
107		vBv += u[i] * v[i]
108		vv += v[i] * v[i]
109	}
110	fmt.Printf("%0.9f\n", math.Sqrt(vBv/vv))
111}
112