h ( ε , ℓ ; r ) = ( 2 π τ A ( ε , ℓ ) 1 − e − 2 π / τ ) 1 2 G ℓ ( − 1 / τ , τ r ) h\left(\epsilon,\ell;r\right)=\left(\frac{2}{\pi\tau}\frac{A(\epsilon,\ell)}{1-e^{-2\pi/\tau}}\right)^{\frac{1}{2}}G_{\ell}\left(-1/\tau,\tau r\right)