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

	/**
	* Evaluates the cumulative distribution function (CDF) for a lognormal distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {Probability} evaluated CDF
	*
	* @example
	* var y = cdf( 2.0 );
	* // returns <number>
	*/
	function cdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x <= 0.0 ) {
			return 0.0;
		}
		return normalCDF( ln(x), mu, sigma );
	}
}
Returns a function for evaluating the cumulative distribution function (CDF) for a lognormal distribution with location parameter `mu` and scale parameter `sigma`.

@param {number} mu - location parameter
@param {PositiveNumber} sigma - scale parameter
@returns {Function} CDF

@example
var cdf = factory( 3.0, 1.5 );

var y = cdf( 1.0 );
// returns ~0.023

y = cdf( 4.0 );
// returns ~0.141