function logpdf( x ) {
		var out;
		if ( isnan( x ) ) {
			return NaN;
		}
		if ( x < 0.0 || x > 1.0 ) {
			// Support of the Beta distribution: [0,1]
			return NINF;
		}
		if ( x === 0.0 ) {
			if ( alpha < 1.0 ) {
				return PINF;
			}
			if ( alpha > 1.0 ) {
				return NINF;
			}
			return ln( beta );
		}
		if ( x === 1.0 ) {
			if ( beta < 1.0 ) {
				return PINF;
			}
			if ( beta > 1.0 ) {
				return NINF;
			}
			return ln( alpha );
		}
		out = -betalnAB;
		out += ( ( alpha-1.0 )*ln(x) ) + ( ( beta-1.0 )*log1p(-x) );
		return out;
	}
Evaluates the natural logarithm of the probability density function (PDF) for a beta distribution.

@private
@param {number} x - input value
@returns {number} evaluated natural logarithm of the PDF

@example
var y = logpdf( 0.3 );
// returns <number>