function mgf( t ) {
		var sigmat;
		var ret;

		if ( isnan( t ) ) {
			return NaN;
		}
		sigmat = t * sigma;
		ret = 1.0 + (sigmat * exp( sigmat*sigmat / 2.0 ));
		ret *= SQRT_HALF_PI * ( erf( sigmat / SQRT2 ) + 1.0 );
		return ret;
	}
Evaluates the moment-generating function (MGF) for a Rayleigh distribution.

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

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