function logcdf( x ) {
		var p;
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x < 0.0 ) {
			return NINF;
		}
		p = -pow( x / lambda, k );
		return ( p < LNHALF ) ? log1p( -exp( p ) ) : ln( -expm1( p ) );
	}
Evaluates the natural logarithm of the cumulative distribution function (CDF) for a Weibull distribution.

@private
@param {number} x - input value
@returns {number} evaluated logCDF

@example
var y = logcdf( 2.0 );
// returns <number>