function entropy( a, b ) {
	if (
		isnan( a ) ||
		isnan( b ) ||
		!isInteger( a ) ||
		!isInteger( b ) ||
		a > b
	) {
		return NaN;
	}
	return ln( b - a + 1 );
}
Returns the entropy of a discrete uniform distribution.

@param {integer} a - minimum support
@param {integer} b - maximum support
@returns {number} entropy

@example
var v = entropy( 0, 1 );
// returns ~0.693

@example
var v = entropy( 4, 12 );
// returns ~2.197

@example
var v = entropy( -4, 4 );
// returns ~2.197

@example
var v = entropy( 1, 2.5 );
// returns NaN

@example
var v = entropy( -0.1, 1 );
// returns NaN

@example
var v = entropy( 2, NaN );
// returns NaN

@example
var v = entropy( NaN, 2 );
// returns NaN