when set to a floating-point value, overrides the default tolerance of
1e-5 for force-field floating-point parameters.
-``GMX_MAX_MPI_THREADS``
- sets the maximum number of MPI-threads that :ref:`gmx mdrun`
- can use.
-
``GMX_MAXCONSTRWARN``
if set to -1, :ref:`gmx mdrun` will
not exit if it produces too many LINCS warnings.