--- /dev/null
+/*
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+ * Redistributions of source code must retain the above copyright
+ notice, this list of conditions and the following disclaimer.
+
+ * Redistributions in binary form must reproduce the above copyright
+ notice, this list of conditions and the following disclaimer in the
+ documentation and/or other materials provided with the distribution.
+
+ * Neither the name of "The Computer Language Benchmarks Game" nor the
+ name of "The Computer Language Shootout Benchmarks" nor the names of
+ its contributors may be used to endorse or promote products derived
+ from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGE.
+*/
+
+/* The Computer Language Benchmarks Game
+ * http://shootout.alioth.debian.org/
+ *
+ * contributed by The Go Authors.
+ * Based on spectral-norm.c by Sebastien Loisel
+ */
+
+package main
+
+import (
+ "flag";
+ "fmt";
+ "math";
+)
+
+var n = flag.Int("n", 2000, "count")
+var nCPU = flag.Int("ncpu", 4, "number of cpus")
+
+func evalA(i, j int) float64 {
+ return 1 / float64(((i + j)*(i + j + 1)>>1+ i + 1));
+}
+
+type Vec []float64
+
+func (v Vec) Times(i, n int, u Vec, c chan int) {
+ for ; i < n; i++ {
+ v[i] = 0;
+ for j := 0; j < len(u); j++ {
+ v[i] += evalA(i, j)*u[j];
+ }
+ }
+ c <- 1;
+}
+
+func (v Vec) TimesTransp(i, n int, u Vec, c chan int) {
+ for ; i < n; i++ {
+ v[i] = 0;
+ for j := 0; j < len(u); j++ {
+ v[i] += evalA(j, i)*u[j];
+ }
+ }
+ c <- 1;
+}
+
+func wait(c chan int) {
+ for i := 0; i < *nCPU; i++ {
+ <-c
+ }
+}
+
+func (v Vec) ATimesTransp(u Vec) {
+ x := make(Vec, len(u));
+ c := make(chan int, *nCPU);
+ for i := 0; i < *nCPU; i++ {
+ go x.Times(i*len(v) / *nCPU, (i+1)*len(v) / *nCPU, u, c);
+ }
+ wait(c);
+ for i := 0; i < *nCPU; i++ {
+ go v.TimesTransp(i*len(v) / *nCPU, (i+1)*len(v) / *nCPU, x, c);
+ }
+ wait(c);
+}
+
+func main() {
+ flag.Parse();
+ 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));
+}