Syntax:
fix ID group-ID print N string
Examples:
fix extra all print 100 "Coords of marker atom = $x $y $z"
Description:
Print a text string to the screen and logfile every N steps during a simulation run. This can be used for diagnostic purposes or even as a debugging tool to monitor some quantity during a run. The text string must be a single argument, so it should be enclosed in double quotes if it is more than one word. If it contains variables ($a thru $z) it must be enclosed in double quotes to insure they are not evaluated when the input script is read, but will instead be evaluated when the string is printed.
See the variable command for a description of equal style variables which are the most useful ones to use with the fix print command, since they are evaluated afresh each timestep that the fix print line is output.
Note that if equal-style variables are used in the print line which contain thermo_style custom keywords for potential energy such as pe, eng, evdwl, ebond, etc, they will only be up-to-date on timesteps where thermodynamics are computed. Hence, if you output thermodynamics every 100 steps, but issue a fix print command with N = 2 that contains such a variable, the printed value will only be current on timesteps that are a multiple of 100. This is because the potential functions in LAMMPS (pairwise, bond, etc) only compute energies on timesteps when thermodynamic output is being performed.
Restrictions: none
Related commands:
Default: none