This is a nonlinear equation, because the permeability of the core, "μ", varies with the magnetic field "B". For an exact solution, the value of "μ" at the "B" value used must be obtained from the core material hysteresis curve. If "B" is unknown, the equation must be solved by numerical methods. However, if the magnetomotive force is well above saturation, so the core material is in saturation, the magnetic field will be approximately the saturation value "Bsat" for the material, and won't vary much with changes in "NI". For a closed magnetic circuit (no air gap) most core materials saturate at a magnetomotive force of roughly 800 ampere-turns per meter of flux path.