Why it is difficult to calculate mmf of air gap of a slotted machine?

Calculating the magnetomotive force (MMF) of the air gap in a slotted machine is challenging due to the complex geometry and the presence of slots, which disrupt the uniform magnetic field. The air gap's magnetic path is not uniform; variations in slot depth and width create non-linearities in the magnetic circuit. Additionally, the fringing effect at the edges of the slots further complicates calculations, as it alters the effective area and permeability of the air gap. These factors make it necessary to use more advanced numerical methods or finite element analysis for accurate MMF calculations.