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Re: [lammps-users] Define average density during simulation
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Re: [lammps-users] Define average density during simulation

From: Steve Plimpton <sjplimp@...24...>
Date: Fri, 23 Jun 2017 08:49:31 -0600

Re: your previous Q:
fix   avload all ave/time 1 100000 1
is invalid, hence the error.  See the fix ave/time doc
page about how to define those 3 numeric values.  The
last one would have to be >= 100000 in this case.

Re: your unexpected output.
I imagine you can debug this yourself
Print v_dal with thermo output.  Verify it
is what you expect at each timestep.
Then output it with fix ave/time with no averaging.
See if the values are the same.
Then expt with some averaging, and check by
hand that the values you now get are the averages
of the single timestep values.  Etc, etc.


On Fri, Jun 23, 2017 at 8:03 AM, alberto <voodoo.bender@...24...> wrote:

I tried to define
variable    dal equal atoms/vol (in real units)


fix   avload all ave/time 1 1 1 v_dal file ave.log

to obtain the comulative average loading

in my case 100 points

the file ave.log report a wrong average

1 0.1
2 0.3
3 0.0


I expect that

Step.   Atoms.  Vol.  Density.   Av
1.        1.     10    0.1.     0.1
2.        3.     10    0.3.     0.2
3         0.     10     0       0.1

Av = ( 0.1+ 0.3) /2 = 0.2

I must define manually _expression_ to calculate it. I can print the results in themo_style ?


2017-06-22 16:17 GMT+02:00 alberto <voodoo.bender@...24...>:

I define a variable
variable    dal equal atoms/vol
and I use fix ave/time as

fix   avload all ave/time 1 100000 1 v_dal ave one,  where 100000 is the total steps of my simulation
but I obtain message error

ERROR: Illegal fix ave/time command


2017-06-21 16:20 GMT+02:00 Steve Plimpton <sjplimp@...24...>:
The fix ave/time command can do averaging with a moving window or cummulative
ave, see its doc page and keywords.


On Tue, Jun 20, 2017 at 2:15 PM, alberto <voodoo.bender@...24...> wrote:
during a gcmc simulation, I produce density of gas per step. I would produce other column with the average density for every n-th step: for second step the average between the first and second, the third as the average between the first, the second, the third, and so on.
I'm a young user of lammps, and on manual I found the keyword fix ave/time command. It's a good idea to produce the results that I wish, or exist other procedure, or it's not possible during lammps run?



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