where Φ(<b>r</b>) is the electric scalar potential, ρ(<b>r</b>) is the volume charge density, and ε = ε<sub>r</sub> ε<sub>0</sub> is the permittivity of the medium.
where <b>A(r)</b> is the magnetic vector potential, <b>J(r)</b> is the volume current density, and μ = μ<sub>r</sub> μ<sub>0</sub> is the permeability of the medium. The magnetic Poisson equation is vectorial in nature and involves a system of three scalar differential equations corresponding to the three components of <b>A(r)</b>.
<math> \mathbf{H(r)} = \frac{1}{\mu} \nabla \times \mathbf{A} (\mathbf{r})</math>
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== A Note on Material and Source Types in EM.Ferma ==