function mgf( t ) {
		if ( t >= 1.0/beta ) {
			return NaN;
		}
		return gamma( 1.0 - (beta * t) ) * exp( mu * t );
	}
Evaluates the moment-generating function (MGF) for a Gumbel distribution.

@private
@param {number} t - input value
@returns {number} evaluated MGF

@example
var y = mgf( 0.5 );
// returns <number>