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### dump_modify command

Syntax:

    dump_modify dump-ID keyword values ...

- dump-ID = ID of dump to modify
- one or more keyword/value pairs may be appended
- keyword = format or scale or image or header or flush or region or thresh

        format arg = C-style format string for one line of output
        scale arg = yes or no
        image arg = yes or no
        flush arg = yes or no
        every arg = N
          N = dump every this many timesteps
        region arg = region-ID or "none"
        thresh args = attribute operation value
          attribute = same attributes (x,fy,etotal,sxx,etc) used by dump custom style
          operation = "<" or "<=" or ">" or ">=" or "==" or "!="
          value = numeric value to compare to
          these 3 args can be replaced by the word "none" to turn off threshholding

Examples:

    dump_modify 1 format "%d %d %20.15g %g %g" scale yes
    dump_modify myDump image yes scale no flush yes
    dump_modify 1 region mySphere thresh x < 0.0 thresh epair >= 3.2

Description:

Modify the parameters of a previously defined dump command. Not all parameters are relevant to all dump styles.

The text-based dump styles have a default C-style format string which simply specifies %d for integers and %g for real values. The format keyword can be used to override the default with a new C-style format string. Do not include a trailing "\n" newline character in the format string. This option has no effect on the dcd and xtc dump styles since they write binary files.

The scale and image keywords apply only to the dump atom style. A scale value of yes means atom coords are written in normalized units from 0.0 to 1.0 in each box dimension. A value of no means they are written in absolute distance units (e.g. Angstroms or sigma). If the image value is yes, 3 flags are appended to each atom's coords which are the absolute box image of the atom in each dimension. For example, an x image flag of -2 with a normalized coord of 0.5 means the atom is in the center of the box, but has passed thru the box boundary 2 times and is really 2 box lengths to the left of its current coordinate. Note that for dump style custom these values can be printed in the dump file by using the appropriate atom attributes in the dump command itself.

The flush option determines whether a flush operation in invoked after a dump snapshot is written to the dump file. A flush insures the output in that file is current (no buffering by the OS), even if LAMMPS halts before the simulation completes. Flushes cannot be performed with dump style xtc.

The every option changes the dump frequency originally specified by the dump command to a new value which must be > 0. The dump frequency cannot be changed for the dump dcd style.

The region keyword only applies to the dump custom style. If specified, only atoms in the region will be written to the dump file. Only one region can be applied as a filter (the last one specified). See the region command for more details. Note that a region can be defined as the "inside" or "outside" of a geometric shape, and it can be the "union" or "intersection" of a series of simpler regions.

The thresh keyword only applies to the dump custom style. Multiple threshholds can be specified. Specifying "none" turns off all threshhold criteria. If theshholds are specified, only atoms whose attributes meet all the threshhold criteria are written to the dump file. The possible attributes that can be tested for are the same as those that can be specified in the dump custom command. Note that different attributes can be output by the dump custom command than are used as threshhold criteria by the dump_modify command. E.g. you can output the coordinates and stress of atoms whose energy is above some threshhold.

Restrictions: none

Related commands:

dump, undump

Default:

The option defaults are format = %d and %g for each integer or floating point value, scale = yes, image = no, flush = yes (except for dump xtc style), region = none, and thresh = none.