{\displaystyle {\begin{aligned}&\nabla \cdot \mathbf {D} =\rho _{f}\\&\nabla \cdot \mathbf {B} =0\\&\nabla \times \mathbf {E} =-{\frac {\partial \mathbf {B} }{\partial t}}\\&\nabla \times \mathbf {H} =\mathbf {J} _{f}+{\frac {\partial \mathbf {D} }{\partial t}}\end{aligned}}}