benchmark/bm_so_spectralnorm.rb

   1 # The Computer Language Shootout
   2 # http://shootout.alioth.debian.org/
   3 # Contributed by Sokolov Yura
   4
   5 def eval_A(i,j)
   6         return 1.0/((i+j)*(i+j+1)/2+i+1)
   7 end
   8
   9 def eval_A_times_u(u)
  10         v, i = nil, nil
  11         (0..u.length-1).collect { |i|
  12                 v = 0
  13                 for j in 0..u.length-1
  14                         v += eval_A(i,j)*u[j]
  15                 end
  16                 v
  17         }
  18 end
  19
  20 def eval_At_times_u(u)
  21         v, i = nil, nil
  22         (0..u.length-1).collect{|i|
  23                 v = 0
  24                 for j in 0..u.length-1
  25                         v += eval_A(j,i)*u[j]
  26                 end
  27                 v
  28         }
  29 end
  30
  31 def eval_AtA_times_u(u)
  32         return eval_At_times_u(eval_A_times_u(u))
  33 end
  34
  35 n = 500 # ARGV[0].to_i
  36
  37 u=[1]*n
  38 for i in 1..10
  39         v=eval_AtA_times_u(u)
  40         u=eval_AtA_times_u(v)
  41 end
  42 vBv=0
  43 vv=0
  44 for i in 0..n-1
  45         vBv += u[i]*v[i]
  46         vv += v[i]*v[i]
  47 end
  48
  49 str = "%0.9f" % (Math.sqrt(vBv/vv)), "\n"
  50 # print str