function entropy( alpha, beta ) {
	if (
		isnan( alpha ) ||
		alpha <= 0.0 ||
		isnan( beta ) ||
		beta <= 0.0
	) {
		return NaN;
	}
	return ln( ( beta/alpha ) * exp( 1.0 + ( 1.0/alpha ) ) );
}
Returns the differential entropy of a Pareto (Type I) distribution.

@param {PositiveNumber} alpha - shape parameter
@param {PositiveNumber} beta - scale parameter
@returns {number} differential entropy

@example
var v = entropy( 1.0, 1.0 );
// returns 2.0

@example
var v = entropy( 4.0, 12.0 );
// returns ~2.349

@example
var v = entropy( 8.0, 2.0 );
// returns ~-0.261

@example
var v = entropy( 1.0, -0.1 );
// returns NaN

@example
var v = entropy( -0.1, 1.0 );
// returns NaN

@example
var v = entropy( 2.0, NaN );
// returns NaN

@example
var v = entropy( NaN, 2.0 );
// returns NaN