# No output with fix ave/time

Hi everyone,
I’d like to compute radial distribution function and output the results by using the `fix ave/time` command, but the output file is empty. This is how I wrote this part of the script:

``````compute		RDF all rdf 200 2 1 3 1 4 1
fix		    RDF_f all ave/time 50 800 50000 c_RDF[*] file rdf.txt mode vector
dump        2 all custom 50 nve/nve.* id type x y z
fix		    3 all nve
run		    50000
unfix		3
unfix		RDF_f
undump		2
``````

To my understanding, the command `fix ave/time` here will compute the rdf values on time steps 10000, 10050, 10100, 10150, …, 50000. However, the rdf.txt was empty after the calculation. If I change the N_{every} from 50 in the script to 10, I can get the rdf values that I want. I think that my understanding of the command `fix ave/time` is not as good as I thought. Could you explain me why I cannot get the rdf values if the N_{every} = 50 ? Please excuse me if the question seems too trivial, and any guidance of this will be highly appreciated.
Sincerely,
Tianze

Whether you get output crucially depends on what is the timestep number when you have the `run 50000` command. Because the output is on multiples of timestep numbers. I.e. with your command, you will have output on timestep 50000, 100000, 150000 but only if there has been enough steps to collect the data. `50*800` means you have to have 40000 steps to collect data, thus if your timestep is larger than 10000 at the beginning of the `run`, then you will only get output on step 100000. That is why reducing nevery will lead to output, because now the data is only collected from step 42000 on instead of step 10000 with nevery = 50.

Hi Akohlmey,
Thank you very much for your kindly reply, it helps a lot. However, I am still a little confused.
First,

Whether you get output crucially depends on what is the timestep number when you have the `run 50000` command.

Do you mean the current time step determines whether I get output? If so, will the simulation portion before `fix ave/time` such as a heating procedure in npt influence the calculation during the `fix ave/time`?
Second,

`50*800` means you have to have 40000 steps to collect data, thus if your timestep is larger than 10000 at the beginning of the `run` , then you will only get output on step 100000.

In my simulation, I have 1670532 timesteps before `fix ave/time`, much more than 40000, but still no output. And I am confused that why I should only get output on step 100000.
Thank you, and any guidance of these questions will be greatly helpful.
Sincerely,
Tianze

Please read the documentation of fix ave/time very carefully. It explains everything.