Hi
I want to calculate the electric dipole moment of point charges along the z-axis with distances a and with the charge distribution
\varrho (\vec{x}) = q \delta (\vec{x}) - 2q \delta (\vec{x} - \vec{a}) + q \delta (\vec{x} - 2 \vec{a})
and of course \vec{a} = a \vec{e}_{z}
I...