${\displaystyle Div\underset{\_}{\underset{\_}{A}}:={\displaystyle \sum _{\mu =0}^3\frac{\partial A_{\mu }}{\partial x_{\mu }}}=\frac{\partial A_0}{\partial \text{j}{c}_{0}t}+div\overrightarrow{A}}$

where $\underset{\_}{\underset{\_}{A}}$ is an arbitrary four-vector

Note 1 to entry: Four-divergence is useful in STR. In general theory of relativity (GTR) for non-flat space-time, a more sophisticated method is used.

Note 2 to entry: The four-divergence of a tensor quantity $Q$ of order $n\ge 1$ is a scalar product of four-nabla and that quantity: $DivQ=◊\cdot Q$ yielding a tensor quantity of order $n-1$.

Note 3 to entry: In the International System of Quantities, the dimension of four-divergence is ${\mathrm{L}}^{-1}$.