function gammaDeltaRatioLanczos( z, delta ) {
	var result;
	var ratio;
	var zgh;

	if ( z < EPSILON ) {
		if ( delta >= FLOAT64_MAX_NTH_FACTORIAL ) {
			ratio = gammaDeltaRatioLanczos( delta, FLOAT64_MAX_NTH_FACTORIAL-delta );
			ratio *= z;
			ratio *= FACTORIAL_169;
			return 1.0 / ratio;
		}
		return 1.0 / ( z * gamma( z+delta ) );
	}
	zgh = z + G - 0.5;
	if ( z + delta === z ) {
		if ( abs( delta / zgh ) < EPSILON ) {
			result = exp( -delta );
		} else {
			result = 1.0;
		}
	} else {
		if ( abs(delta) < 10.0 ) {
			result = exp( ( 0.5-z ) * log1p( delta/zgh ) );
		} else {
			result = pow( zgh / (zgh+delta), z-0.5 );
		}
		// Split up the calculation to avoid spurious overflow:
		result *= lanczosSum( z ) / lanczosSum( z + delta );
	}
	result *= pow( E / ( zgh+delta ), delta );
	return result;
}
Calculates the ratio of two gamma functions via Lanczos approximation.

## Notes

-   When \\( z < \epsilon \\), we get spurious numeric overflow unless we're very careful. This can occur either inside `lanczosSum(z)` or in the final combination of terms. To avoid this, split the product up into 2 (or 3) parts:

    ```tex
    \begin{align*}
    G(z) / G(L) &= 1 / (z \cdot G(L)) ; z < \eps, L = z + \delta = \delta \\
    z * G(L) &= z * G(lim) \cdot (G(L)/G(lim)) ; lim = \text{largest factorial}
    \end{align*}
    ```

@private
@param {number} z - first gamma parameter
@param {number} delta - difference
@returns {number} gamma ratio