[lammps-users] Fix nph

Hi Steve,
Does nph still have NULL as not-controlled as a choice ?
Since the change, I did not see that on the documentation.
It used to be there.

In the current version of fix nph and fix npt, you specify
exactly what components of the 6-element stress tensor
you want to control. So there is no need for a NULL.
If you don't specify a component, it won't be controlled,
same as NULL was before.