1 // The Great Computer Language Shootout

     2 // http://shootout.alioth.debian.org/

     3 //

     4 // contributed by Ian Osgood

     5 

     6 function A(i,j) {

     7   return 1/((i+j)*(i+j+1)/2+i+1);

     8 }

     9 

    10 function Au(u,v) {

    11   for (var i=0; i<u.length; ++i) {

    12     var t = 0;

    13     for (var j=0; j<u.length; ++j)

    14       t += A(i,j) * u[j];

    15     v[i] = t;

    16   }

    17 }

    18 

    19 function Atu(u,v) {

    20   for (var i=0; i<u.length; ++i) {

    21     var t = 0;

    22     for (var j=0; j<u.length; ++j)

    23       t += A(j,i) * u[j];

    24     v[i] = t;

    25   }

    26 }

    27 

    28 function AtAu(u,v,w) {

    29   Au(u,w);

    30   Atu(w,v);

    31 }

    32 

    33 function spectralnorm(n) {

    34   var i, u=[], v=[], w=[], vv=0, vBv=0;

    35   for (i=0; i<n; ++i) {

    36     u[i] = 1; v[i] = w[i] = 0;

    37   }

    38   for (i=0; i<10; ++i) {

    39     AtAu(u,v,w);

    40     AtAu(v,u,w);

    41   }

    42   for (i=0; i<n; ++i) {

    43     vBv += u[i]*v[i];

    44     vv  += v[i]*v[i];

    45   }

    46   return Math.sqrt(vBv/vv);

    47 }

    48 

    49 for (var i = 6; i <= 48; i *= 2) {

    50     spectralnorm(i);

    51 }