Output time at which a condition is met

Dear all,

I have assigned a set of atoms to a particular group and defined a region of space in my input script. Originally, all the atoms from the group are outside the region. When I run a simulation, some atoms from the group may enter the region. I want to determine the time-step at which any atom from the group first enters the region. Is it possible to do this without outputting the number of atoms in the region every time-step? I have managed to accomplish this using fix halt but I am wondering if there is an easier way without stopping the simulation.


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You could define a variable that uses the count(group) function

and test when it becomes non-zero. Something like a run every

command where every step you invoke and if test on the

variable and print something out when it happens.