1 d3.random = {

     2   normal: function(mean, deviation) {

     3     if (arguments.length < 2) deviation = 1;

     4     if (arguments.length < 1) mean = 0;

     5     return function() {

     6       var x, y, r;

     7       do {

     8         x = Math.random() * 2 - 1;

     9         y = Math.random() * 2 - 1;

    10         r = x * x + y * y;

    11       } while (!r || r > 1);

    12       return mean + deviation * x * Math.sqrt(-2 * Math.log(r) / r);

    13     };

    14   }

    15 };