http://rogercortesi.com/eqn/index.php

\Delta_{i+1}=\frac{1}{\sqrt{\frac{\rho^*}{\rho^c}}}\Delta_{i}

\rho^c=\frac{A_\odot}{A_\square}

\rho^*-0.20<\rho^c<\rho^*+0.20

2\Delta_{i+1}