function mgf( t, mu, sigma ) {
	if (
		isnan( t ) ||
		isnan( mu ) ||
		isnan( sigma ) ||
		sigma <= 0.0
	) {
		return NaN;
	}
	return exp( (mu * t) + (0.5 * pow( sigma * t, 2.0 )) );
}
Evaluates the moment-generating function (MGF) for a normal distribution with mean `mu` and standard deviation `sigma` at a value `t`.

@param {number} t - input value
@param {number} mu - mean
@param {PositiveNumber} sigma - standard deviation
@returns {number} evaluated MGF

@example
var y = mgf( 2.0, 0.0, 1.0 );
// returns ~7.389

@example
var y = mgf( 0.0, 0.0, 1.0 );
// returns 1.0

@example
var y = mgf( -1.0, 4.0, 2.0 );
// returns ~0.1353

@example
var y = mgf( NaN, 0.0, 1.0 );
// returns NaN

@example
var y = mgf( 0.0, NaN, 1.0 );
// returns NaN

@example
var y = mgf( 0.0, 0.0, NaN );
// returns NaN

@example
var y = mgf( 2.0, 0.0, 0.0 );
// returns NaN