 When the input-to-output gain is very large, the equivalent input-to-ground impedance is very small while the output-to-ground impedance is essentially equal to the original (input-to-output) impedance.Calculating the capacitance of a system amounts to solving the Laplace equation "∇2φ = 0" with a constant potential "φ" on the 2-dimensional surface of the conductors embedded in 3-space.This is simplified by symmetries.