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

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

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