code: function getCDF( mu, s2 ) {
  		var A = 1 / 2,
  			B = Math.sqrt( s2*2 );
  		/**
  		* FUNCTION: cdf( x )
  		*	Evaluates the cumulative distribution function at input value `x`.
  		*
  		* @private
  		* @param {Number} x - input value
  		* @returns {Number} evaluated CDF
  		*/
  		return function cdf( x ) {
  			var C = x - mu;
  			return A * ( 1 + erf( C / B ) );
  		};
  	}
docs: end FUNCTION getPDF() 
  FUNCTION: getCDF( mu, variance )
  Returns a cumulative density function for a normal distribution with mean `mu` and variance `s2`.
  
  @private
  @param {Number} mu - distribution mean
  @param {Number} variance - distribution variance
  @returns {Function} cumulative density function (CDF)