Syntax:
-fix ID group-ID ave/time Nevery Nrepeat Nfreq style ID type file +fix ID group-ID ave/time Nevery Nrepeat Nfreq style ID keyword args ...-
type arg = scalar or vector or both + scalar = single scalar value from fix or compute + vector = vector of values from fix or compute + both = both a single value and vector of values from fix or compute + file arg = filename + filename = file to write results to + ave args = one or running or window M + one = output new average value every Nfreq steps + running = output cummulative average of all previous Nfreq steps + window M = output average of M most recent Nfreq steps ++
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 +fix 1 all ave/time 100 5 1000 compute myTemp +fix 1 all ave/time 100 5 1000 compute myTemp ave window 20 +fix 1 all ave/time 1 100 1000 fix indenter value both file temp.indentDescription:
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. +be used by other output commands such as +thermo_style custom, and also written to a file.
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 +quantities cannot be averaged with this fix; their values can be +averaged by the fix ave/spatial or fix ave/atom commands.
+Since the calculation is performed by the compute or fix which stores +its own "group" definition, the group specified as part of the fix +ave/time command is ignored. +
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 +"per-atom" compute. The compute 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 @@ -62,35 +87,61 @@ 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 on timestep 100. Similary for timesteps -190,192,194,196,198,200 on timestep 200, etc. +
The Nevery, Nrepeat, and Nfreq arguments specify on what +timesteps the property will be evaluated in order to contribute to the +average. 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. +Nfreq must be a multiple of Nevery and Nevery must be non-zero +even if Nrepeat is 1.
-The type 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. If -file output is specified, all N values are written to the file at each -output. +
For example, 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 +on timestep 100. Similary for timesteps 190,192,194,196,198,200 on +timestep 200, etc.
-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. +
+ +Additional optional keywords also affect the averaging.
-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. +
The type keyword chooses whether the scalar and/or vector quantities +produced by the compute or fix are used. For a setting of scalar a +single global value is used. For a setting of vector N global +values are used, where N is defined by the compute or fix, e.g. 6 +pressure tensor components. For a setting of both, both a scalar +the vector values are used. When vectors are used, each of the N +values is averaged independently.
+The file keyword allows a filename to be specified. The scalar +and/or N vector quantities are written to the file in a +self-explanatory text format. +
+The ave keyword determines how the scalar and/or vector values +produced every Nfreq steps are averaged with each other before they +are accessed by another output command or written to a file. +
+If the ave setting is one, then the values produced on timesteps +that are multiples of Nfreq are independent of each other; they are +output as-is without further averaging. +
+If the ave setting is running, then the values produced on +timesteps that are multiples of Nfreq are summed and averaged in a +cummulative sense before being output. Each output value is thus the +average of the value on that timestep with all preceeding values. +This running average begins when the fix is defined; it can only be +restarted by deleting the fix via the unfix command, or +re-defining the fix by re-specifying it. +
+If the ave setting is window, then the values produced on +timesteps that are multiples of Nfreq are summed and averaged within +a moving "window" of time, so that the last M values are used to +produce the output. E.g. if M = 3 and Nfreq = 1000, then the output +on step 10000 will be the average of the individual values on steps +8000,9000,10000. Outputs on early steps will average over less than M +values if they are not available. +
+
+Restart, fix_modify, output, run start/stop, minimize info:
No information about this fix is written to binary restart @@ -101,13 +152,22 @@ are relevant to this fix. scalar and/or a vector of quantities which can be accessed by various output commands. The values should only be accessed on timesteps that are multiples of Nfreq since that is when -averaging is complete. +averaging is performed.
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 +
Restrictions: +
+If the style is compute and the specified 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.
Related commands:
@@ -116,4 +176,6 @@ ave/spatialDefault: none
+The option defaults are style = scalar, no file output, and ave = one. +