function mean( p ) {
	if (
		isnan( p ) ||
		p < 0.0 ||
		p > 1.0
	) {
		return NaN;
	}
	return ( 1.0 - p ) / p;
}
Returns the expected value of a geometric distribution.

@param {Probability} p - success probability
@returns {NonNegativeNumber} expected value

@example
var v = mean( 0.1 );
// returns 9.0

@example
var v = mean( 0.5 );
// returns 1.0

@example
var v = mean( 1.1 );
// returns NaN

@example
var v = mean( NaN );
// returns NaN