function factory( mu ) {
	if ( isnan( mu ) ) {
		return constantFunction( NaN );
	}
	return logcdf;

	/**
	* Evaluates the natural logarithm of the cumulative distribution function (logCDF) of a degenerate distribution.
	*
	* @private
	* @param {number} x - input value
	* @returns {number} natural logarithm of cumulative distribution function
	*
	* @example
	* var y = logcdf( 10.0 );
	* // returns <number>
	*/
	function logcdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		return ( x < mu ) ? NINF : 0.0;
	}
}
Returns a function for evaluating the natural logarithm of the cumulative distribution function (logCDF) of a degenerate distribution centered at a provided mean value.

@param {number} mu - value at which to center the distribution
@returns {Function} logCDF

@example
var logcdf = factory( 5.0 );

var y = logcdf( 3.0 );
// returns -Infinity

y = logcdf( 6.0 );
// returns 0.0

y = logcdf( NaN );
// returns NaN