The vortex states in ferromagnetic or antiferromagnetic material are also important, mainly for information technology They are exceptional, since in contrast to superfluids or superconducting material one has a more subtle mathematics: instead of the usual equation of the type curl ⁡ ⁡ v → → ( x , y , z , t ) ∝ ∝ Ω Ω → → ( r , t ) ⋅ ⋅ δ δ ( x , y ) , where Ω Ω → → ( r , t ) is the vorticity at the spatial and temporal coordinates, and where δ δ ( x , y ) is the Dirac function, one has: