From 758267254d204e61ea1ac81d00d9cd814aff8448 Mon Sep 17 00:00:00 2001
From: pverghese <p.verghese@gmail.com>
Date: Sat, 6 Jul 2019 19:59:50 +0530
Subject: [PATCH] Added Benchmark-games: spectralnorm

---
 examples/spectral.v | 73 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 examples/spectral.v

diff --git a/examples/spectral.v b/examples/spectral.v
new file mode 100644
index 0000000000..dd72f553fe
--- /dev/null
+++ b/examples/spectral.v
@@ -0,0 +1,73 @@
+/*
+https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/spectralnorm.html
+Added: Pradeep Verghese
+
+*/
+
+module main
+import math
+import os
+
+
+fn evala(i, j int) int {
+    return ((i+j)*(i+j+1)/2 + i + 1)
+}
+
+fn (v mut []f64) times(u []f64) {
+    for i := 0; i < v.len; i++ {
+        mut a := f64(0)
+        for j :=0; j< u.len; j++ {
+            a += u[j] /f64(evala(i,j))
+        }
+        v[i] = a
+    }
+}
+
+fn (v mut []f64) times_trans(u []f64) {
+    for i := 0; i< v.len; i++ {
+        mut a := f64(0)
+        for j :=0; j< u.len; j++ {
+            a += u[j] / f64(evala(j,i))
+        }
+        v[i] = a
+    }
+}
+
+fn (v mut []f64) a_times_transp(u []f64) {
+    mut x := [f64(0); u.len]
+    x.times(u)
+    v.times_trans(x)
+} 
+
+fn main() {
+
+    args := os.args
+    mut n := int(0)
+
+    if args.len == 2 {
+        n = args[1].int()
+    }
+    else {
+        n = 0 
+    }
+    mut u := [f64(1.0);n]
+    mut v := [f64(1.0);n]
+
+    for i := 0; i< 10; i++ {
+        v.a_times_transp(u)
+        u.a_times_transp(v)
+    }
+
+    mut vbv := f64(0)
+    mut vv  := f64(0)
+
+    for i :=0; i< n; i++ {
+        vbv += u[i] * v[i]
+        vv += v[i] * v[i]
+    }
+    ans := math.sqrt(vbv/vv)
+
+    println('${ans:0.9f}')
+
+
+}