information:filtering
Diffusion equation

Taking the curl on both sides of this equation and then using a common vector calculus identity for the curl of the curl results in ∇ (∇ ⋅ H) − ∇ 2 H = ∇ × J. {\displaystyle \nabla \left(\nabla \cdot \mathbf {H} \right)-\nabla ^{2}\mathbf {H} =\nabla \times \mathbf {J}.}