function factory( alpha, beta ) {
	if (
		isnan( alpha ) ||
		isnan( beta ) ||
		alpha <= 0.0 ||
		beta <= 0.0
	) {
		return constantFunction( NaN );
	}
	return cdf;

	/**
	* Evaluates the cumulative distribution function (CDF) for a Pareto (Type I) distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {Probability} evaluated CDF
	*/
	function cdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x < beta ) {
			return 0.0;
		}
		return 1.0 - pow( beta / x, alpha );
	}
}
Returns a function for evaluating the cumulative distribution function (CDF) for a Pareto (Type I) distribution with shape parameter `alpha` and scale parameter `beta`.

@param {PositiveNumber} alpha - shape parameter
@param {PositiveNumber} beta - scale parameter
@returns {Function} CDF

@example
var cdf = factory( 10.0, 2.0 );
var y = cdf( 3.0 );
// returns ~0.983

y = cdf( 2.5 );
// returns ~0.893