function mgf( t ) {
		var bt;
		if ( abs( t ) >= 1.0/b ) {
			return NaN;
		}
		bt = b * t;
		return exp( mu * t ) / ( 1.0 - pow( bt, 2.0 ) );
	}
Evaluates the moment-generating function (MGF) for a Laplace (double exponential) distribution.

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

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