function mgf( t ) {
		if ( isnan( t ) ) {
			return NaN;
		}
		return expm1( -lambda ) / expm1( t - lambda );
	}
Evaluates the moment-generating function (MGF) for a Planck distribution.

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

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