code: function cdf( x, alpha, beta ) {
  	if ( x < beta ) {
  		return 0;
  	}
  	return 1 - pow( beta / x, alpha );
  }
docs: CDF // 
  FUNCTION: cdf( x, alpha, beta )
  Evaluates the cumulative distribution function (CDF) for a Pareto distribution with shape parameter `alpha` and scale parameter `beta` at a value `x`.
  
  @param {Number} x - input value
  @param {Number} alpha - shape parameter
  @param {Number} beta - scale parameter
  @returns {Number} evaluated CDF