Hello,
in statistics, one can derive the moments of a distribution by using a generating function
[tex]<x^n> = \int dx x^n f(x) = \left( \frac {d}{dt} \int dx \exp(tx) f(x) \right)_{t=0} = \left( \frac d {dt} M(t) \right)_{t=0}[/tex]
Is there a similar method to derive the multipole moments in electrodynamics, e.g. is there a generating function? I know that the multipole moments are derived from the expansion of
[tex]\frac {1}{\leftx\right}[/tex]
but I don't seem to get the connection to a generating function.
