function mgf( t, lambda ) {
	return addon( t, lambda );
}
Evaluates the moment-generating function (MGF) for an exponential distribution with rate parameter `lambda` at a value `t`.

@private
@param {number} t - input value
@param {PositiveNumber} lambda - rate parameter
@returns {number} evaluated MGF

@example
var v = mgf( 2.0, 3.0 );
// returns 3.0

@example
var v = mgf( 0.4, 1.2 );
// returns 1.5

@example
var v = mgf( 0.8, 1.6 );
// returns 2.0

@example
var v = mgf( 4.0, 3.0 );
// returns NaN

@example
var v = mgf( NaN, 3.0 );
// returns NaN

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