Dear Steve, Lammps Users,

A very happy new year to all of you.

I am having some problem in understanding the compute sum command. In the doc page of compute_stress_atom, it is mentioned that one can calculate global stress vector as follows.

compute peratom all stress/atom

compute p all sum peratom

variable p equal div(add(add(c_p**1**,c_p**2**),c_p**3**),mult(3.0,vol))

thermo_style custom step temp etotal c_global v_p

When I tried it on my inputscript, I got an error on the second compute command. Here, the compute compute doesnâ€™t seem to be working. I looked at the code (compute_sum.cpp) and understood that probably the command should be written in the following manner.

compute p all sum c_peratom[1] c_peratom[2] c_peratom[3] c_peratom[4] c_peratom[5] c_peratom[6]

This command seems to be working with latest (3rd Jan version). I just want to make sure that I am going the right way. In that case, I doc page could be clarified, If I am misunderstanding something please let me know.

If my version of compute is correct, does it mean that p[1] would be sum of all stress/atom for peratom[1], same for the case with p[2], p[3], etc? In such case, is it fine to define the variable command as

variable p equal div(add(add(c_p **1**,c_p**2**),c_p**3**),mult(3.0,vol))

or one should define it as

variable p equal div(add(add(c_p[**1]**,c_p[**2]**),c_p[**3]**),mult(3.0,vol))

Any comments will be highly appreciated.

Regards,

Vikas