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

	/**
	* Evaluates the natural logarithm of the cumulative distribution function (CDF) for a Pareto (Type I) distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} evaluated logCDF
	*/
	function logcdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x < beta ) {
			return NINF;
		}
		return log1p( -pow( beta / x, alpha ) );
	}
}
Returns a function for evaluating the natural logarithm of 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} logCDF

@example
var logcdf = factory( 10.0, 2.0 );
var y = logcdf( 3.0 );
// returns ~-0.017

y = logcdf( 2.5 );
// returns ~-0.114