function logcdf( x ) {
		if ( isnan( x ) ) {
			return NaN;
		}
		return ( x < mu ) ? NINF : 0.0;
	}
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>