function factory( k, lambda ) {
	var lnkl;
	if (
		isnan( k ) ||
		isnan( lambda ) ||
		k <= 0.0 ||
		lambda <= 0.0
	) {
		return constantFunction( NaN );
	}
	lnkl = ln( k / lambda );
	return logpdf;

	/**
	* Evaluates the natural logarithm of the probability density function (PDF) for a Weibull distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} evaluated logPDF
	*
	* @example
	* var y = logpdf( 2.3 );
	* // returns <number>
	*/
	function logpdf( x ) {
		var xol;
		if ( x < 0.0 ) {
			return NINF;
		}
		if ( x === PINF || x === NINF ) {
			return NINF;
		}
		if ( x === 0.0 ) {
			return ( k === 1.0 ) ? ln( k / lambda ) : NINF;
		}
		xol = x / lambda;
		return lnkl + ( ( k - 1.0 ) * ln( xol ) ) - pow( xol, k );
	}
}
Returns a function for evaluating the natural logarithm of the probability density function (PDF) for a Weibull distribution.

@param {PositiveNumber} k - shape parameter
@param {PositiveNumber} lambda - scale parameter
@returns {Function} function to evaluate the logarithm of the probability density function

@example
var logpdf = factory( 7.0, 6.0 );
var y = logpdf( 7.0 );
// returns ~-1.863

y = logpdf( 5.0 );
// returns ~-1.219