I am confused about the Nevery, Nrepeat, and Nfreq arguments in fix ave/chunk command

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1

Hi lammps users
I am confused about the Nevery, Nrepeat, and Nfreq arguments in fix ave/chunk command. I used the following command
fix profile water ave/chunk 1 10 10 chunky vx file vx.profile

According to the manual, the value of vx on timestep 1,2,3…9,10 will be used to calculate the time averaged vx and this time averaged value will used as the output on timestep 10. Also, the time averaged vx over timestep 11,12,13…18,19.20 will used as the output of timestep 20. And the time averaged vx on timestep 10 and 20 will be written into the vx.profle file.

However, there is only value on timestep 20 when I check the output file. Is there something wrong with my understanding of those arguments? If my understanding is right, why there is just value on timestep 20?

Fan Li

2

Those values were used to average, what you would get is only the average that was calculated as output

Santo

3

Hi Santo
I think my understanding is right from your answer. But I should get the two averaged values for 10 and 20 timestep separately. But I only got one for 20, what is wrong?

4

Did you have a minimization before the fix ave/chunk run? Did your run start at a step other than zero (and perhaps less than 10)? If yes, then fix ave would output averages at the next “full” integer, which is 20 in this case.

Ray

5

Hi Ray
Yes, I did minimization. Thanks for your answer.
Fan Li

6

This is a good reason to follow the minimize with:

reset_timestep 0