  To model ferromagnetic material in finite element analysis a correct
description of the constitutive relationship (BH-law) must be found from
measured data. This article proposes to use the energy density function as a
centrepiece. Using this function, which turns out to be a convex function of
the flux density, guarantees energy conservative modelling. The magnetic field
strength can be seen as a derivative with respect to the flux density.
Especially for anisotropic materials (from lamination and/or grain orientation)
this method has advantages. Strictly speaking this method is only valid for
anhysteretic and thermodynamically stable material.
