A simulation of a WCA fluid under constant volume uniaxial strain
with stretching in the z direction, compression in the x and y
directions.The xx, yy and zz components of the pressure tensor are 
written to the log file. The simulation conditions are the same 
used in the paper by Thomas Hunt [http://arxiv.org/abs/1310.3905]
and should yield an zz pressure near 5 and xx/yy pressures near 10.

A simulation of a WCA fluid under stress-controlled biaxial strain 
with stretching in the x and y directions, compression in the z 
direction. The zz stress is controlled using the ext keyword in fix
npt/uef. The xx yy and zz components of the pressure tensor are 
written to the log file. The simulations conditions should yield 
xx/yy pressures near 5 and zz pressure near 10