This is a test case for field solver. It initialized proton
distribution so that it has a constant speed (all three components) in
a box that is periodic in all three coordinates.
The magnetic field is a 'cross' centered at the origin. At the end of
the simulation the magnetic field has been translated one full period,
i.e., ideally the final state should be the same as the initial state. 

This test case tests for errors
- field solver code: E,B,wave speeds,dt calculation,etc.

This test case does not test errors in
- vlasov acceleration
- vlasov translation
- boundary conditions (field or vlasov)

You should compare either the magnetic field or electric field values to 
the reference values. Since E and B depend on each others it does not make 
sense to compare both.
