/** Store all the statistical functions used **/ 

/** 
	Returns a gaussian random function with the given mean and stdev.
	Note that this returns a function, not a value. 
**/
function gaussian(mean, stdev) {
    var y2;
    var use_last = false;
    return function() {
        var y1;
        if(use_last) {
           y1 = y2;
           use_last = false;
        }
        else {
            var x1, x2, w;
            do {
                 x1 = 2.0 * Math.random() - 1.0;
                 x2 = 2.0 * Math.random() - 1.0;
                 w  = x1 * x1 + x2 * x2;               
            } while( w >= 1.0);
            w = Math.sqrt((-2.0 * Math.log(w))/w);
            y1 = x1 * w;
            y2 = x2 * w;
            use_last = true;
       }

       var retval = mean + stdev * y1;
       return retval;
   }
}