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

	/**
	* Evaluates the natural logarithm of the cumulative distribution function (CDF) for a Kumaraswamy's double bounded distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} evaluated logCDF
	*
	* @example
	* var y = logcdf( 2.0 );
	* // returns <number>
	*/
	function logcdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x <= 0.0 ) {
			return NINF;
		}
		if ( x >= 1.0 ) {
			return 0.0;
		}
		return ln( 1.0 - pow( 1.0 - pow( x, a ), b ) );
	}
}
Returns a function for evaluating the cumulative distribution function (CDF) for a Kumaraswamy's double bounded distribution with first shape parameter `a` and second shape parameter `b`.

@param {PositiveNumber} a - first shape parameter
@param {PositiveNumber} b - second shape parameter
@returns {Function} CDF

@example
var logcdf = factory( 0.5, 0.5 );

var y = logcdf( 0.8 );
// returns ~-0.393

y = logcdf( 0.3 );
// returns ~-1.116