Problem description:

An iron divided tube in homogeneous magnetic field in the air.Direction
of the field's vector is North-South.Problem is a plane nonlinear of 
magnetostatics, plane XY.


Geometry of the tube:
 
       Inner diameter = 50 mm;
       Outer diameter = 60 mm;
       Air gap = 5 mm.

Material parameters:

       Permeability of the air = 1 Mu0, relative;
       Permeability of the tube is gived by B-H curve.

       Coercive force of the air  Hcy = 10000 A/m.


