function mean( mu ) {
	return mu;
}
Returns the expected value of a degenerate distribution.

@param {number} mu - constant value of distribution
@returns {number} expected value

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

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

@example
var v = mean( 10.0 );
// returns 10.0

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