This is a test case for Vlasov translation operator.

The distribution is translated with a constant 
speed to +x,+y direction for roughly one period (dynamic
timestepping). Initially the box is empty, and plasma is flowing in
from -x and -y boundaries. Outflow conditions are used for +x,+y
boundaries, and in z-direction the box is periodic.

This test case tests for errors
- Vlasov translation
- dynamic timestepping
- sparse velocity machinery
- Maxwell and outflow boundary conditions

This test case does not test errors in
- vlasov acceleration
- field propagators

You can compare the density 'rho' or the velocity block data 'proton'
against the reference values.

