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Re: [lammps-users] summing too many variables in a loop
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Re: [lammps-users] summing too many variables in a loop

From: Axel Kohlmeyer <akohlmey@...24...>
Date: Fri, 14 Jul 2017 20:05:49 -0400

On Fri, Jul 14, 2017 at 7:40 PM, Mostafa Nejatolahi <mostafa.nejatolahi@...24...> wrote:
Hello all,

I will be appreciated if someone tells me a way to calculate a summation like the following in a shorter way (the number of variables could be higher like 81, 125, ...).

variable        Jx equal v_Jx1+v_Jx2+v_Jx3+v_Jx4+v_Jx5+v_Jx6+v_Jx7&

I used a loop-next-jump command but I got this error:
ERROR: Variable has circular dependency (../variable.cpp:1823)

variable sum equal 0 
variable i loop 27 
label start_of_loop_5 
variable sum equal v_sum+v_Jx$i
jump SELF start_of_loop_5 

​you can escape the circular dependency by using an immediate expansion ​in between to carry the sum value to the next loop. check this out:

cat in.loopme

variable i1 equal 1
variable i2 equal 10
variable i3 equal 100
variable i4 equal 1000

variable sum equal 0.0
variable i loop 4
label  loop
variable hold equal ${sum}
variable sum equal v_hold+v_i$i
print "i=$i sum=${sum}"
next i
jump SELF loop

print "final sum=${sum}"


p.s.: please note, that any input in LAMMPS that requires *that* many variables is probably doing something that is much simpler and more efficiently (and more likely correctly) done in post-processing. script languages like python are much more suitable for such tasks. please also note, that recent LAMMPS versions, if compiled accordingly, also support python style variables to embed python scriptlets.




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Dr. Axel Kohlmeyer  akohlmey@...24...
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.