I know that in the vector potential formulation one can use a scalar Green function (to find the said potential and from then on the electric and magnetic fields), and that this works because the components of the potential are in the same direction as those of the source - i.e. a current in the x-direction will give you the x-component of the potential. I also know that this is no longer true if instead of a differential equation involving the vector potential, we use equations involving the fields, and this is why we have to use a dyadic Green function in this case rather than a scalar one. My question is: what do the columns and rows of the dyadic represent? I assume one index represents the direction of the component of the Green's function itself, i.e. the direction of the component of the field due to a unit idealized differential bit of current? And the other index represents the component of the differential bit of current responsible for that dyadic element? For instance, Gxy would be the x component of the field due to the y component of the source current (or the other way around?)? Is that right, and if so which index represents what?