paragraph_text: <td align=center><math>\begin{matrix} \left(\Delta A_r - {2 A_r \over r^2} - {2 \over r^2\sin\vartheta}{\partial \left(A_\vartheta \sin\vartheta\right) \over \partial\vartheta} - {2 \over r^2\sin\vartheta}{\partial A_\varphi \over \partial \varphi}\right) \boldsymbol{\hat r} & + \\ \left(\Delta A_\vartheta - {A_\vartheta \over r^2\sin^2\vartheta} + {2 \over r^2}{\partial A_r \over \partial \vartheta} - {2 \cos\vartheta \over r^2\sin^2\vartheta}{\partial A_\varphi \over \partial \varphi}\right) \boldsymbol{\hat\vartheta} & + \\ \left(\Delta A_\varphi - {A_\varphi \over r^2\sin^2\vartheta} + {2 \over r^2\sin\vartheta}{\partial A_r \over \partial \varphi} + {2 \cos\vartheta \over r^2\sin^2\vartheta}{\partial A_\vartheta \over \partial \varphi}\right) \boldsymbol{\hat\varphi} & \end{matrix}</math>