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fix ave/time command

Syntax:

fix ID group-ID ave/time Nevery Nrepeat Nfreq style ID flag file 

Examples:

fix 1 all ave/time 100 5 1000 compute myTemp 0 temp.stats
fix 1 all ave/time 1 100 1000 fix indenter 0 temp.indent 

Description:

Calculate one or more instantaneous quantities every few timesteps, and average them over a longer timescale. The resulting averages can be written to a file and/or used by other output commands such as thermo_style custom.

This fix can be used to time-average a compute which calculates a global quantity such as a temperature or pressure or a fix which calculates a global quantity. Note that per-atom computes cannot be used with this fix; their values can be averaged by the fix ave/spatial or fix ave/atom commands.

For style compute the ID specifies a compute which calculates the desired property. The compute must be a "global" compute that calculates one or more global properties rather than a "per-atom" compute. The fix must be previously defined in the input script. Or it can be a compute defined by thermodynamic output or other fixes such as fix nvt or fix temp/rescale. Users can write code for their own compute styles and add them to LAMMPS.

For style fix the ID specifies a fix which calculates the desired property. The fix must calculate a global scalar or vector quantity, which only a few fixes do. See the doc page for individual fix commands for details. The fix must be previously defined in the input script. Users can write code for their own fix styles and add them to LAMMPS.

The Nevery, Nrepeat, and Nfreq arguments specify how the property will be time-averaged. The final averaged value(s) are computed every Nfreq timesteps. The average is over Nrepeat values, computed in the preceeding portion of the simulation every Nevery timesteps. Thus if Nevery=2, Nrepeat=6, and Nfreq=100, then values on timesteps 90,92,94,96,98,100 will be used to compute the final average written to the file on timestep 100. Similary for timesteps 190,192,194,196,198,200 on timestep 200, etc.

The flag argument chooses whether the scalar and/or vector calculation of the compute or fix is invoked. The former computes a single global value. The latter computes N global values, where N is defined by the compute or fix, e.g. 6 pressure tensor components. In the vector case, each of the N values is averaged independently and N values are written to the file at each output.

Since the calculation is performed by the compute or fix which stores its own "group" definition, the group specified for with the fix ave/time command is ignored.

If the style is compute and the compute calculates pressure, it will cause the force computations performed by LAMMPS (pair, bond, angle, etc) to calculate virial terms each Nevery timesteps. If this is more frequent than thermodynamic output, this adds extra cost to a simulation. However, if a constant pressure simulation is being run (fix npt or fix nph), LAMMPS is already calculating virial terms for the pressure every timestep.

Restart, fix_modify, output, run start/stop, minimize info:

No information about this fix is written to binary restart files. None of the fix_modify options are relevant to this fix. No global scalar or vector or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is not invoked during energy minimization.

Restrictions: none

Related commands:

compute, fix ave/atom, fix ave/spatial

Default: none