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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
</CENTER>
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<H3>dump_modify command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>dump_modify dump-ID keyword values ...
</PRE>
<UL><LI>dump-ID = ID of dump to modify
<LI>one or more keyword/value pairs may be appended
<LI>keyword = <I>format</I> or <I>scale</I> or <I>image</I> or <I>flush</I> or <I>unwrap</I> or <I>every</I> or <I>precision</I> or <I>region</I> or <I>thresh</I>
<PRE> <I>format</I> arg = C-style format string for one line of output
<I>scale</I> arg = <I>yes</I> or <I>no</I>
<I>image</I> arg = <I>yes</I> or <I>no</I>
<I>flush</I> arg = <I>yes</I> or <I>no</I>
<I>unwrap</I> arg = <I>yes</I> or <I>no</I>
<I>every</I> arg = N
N = dump every this many timesteps
<I>precision</I> arg = power-of-10 value from 10 to 1000000
<I>region</I> arg = region-ID or "none"
<I>thresh</I> 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 thresholding
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>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
dump_modify xtcdump precision 10000
</PRE>
<P><B>Description:</B>
</P>
<P>Modify the parameters of a previously defined dump command. Not all
parameters are relevant to all dump styles.
</P>
<P>The text-based dump styles have a default C-style format string which
simply specifies %d for integers and %g for real values. The <I>format</I>
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 <I>dcd</I> and <I>xtc</I> dump
styles since they write binary files.
</P>
<P>The <I>scale</I> and <I>image</I> keywords apply only to the dump <I>atom</I> style.
A scale value of <I>yes</I> means atom coords are written in normalized
units from 0.0 to 1.0 in each box dimension. A value of <I>no</I> means
they are written in absolute distance units (e.g. Angstroms or sigma).
If the image value is <I>yes</I>, 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 <I>custom</I> these values
can be printed in the dump file by using the appropriate atom
attributes in the dump command itself.
</P>
<P>The <I>flush</I> 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 <I>xtc</I>.
</P>
<P>The <I>unwrap</I> option only applies to the dump <I>dcd</I> and <I>xtc</I> styles.
If set to <I>yes</I>, coordinates will be written "unwrapped" by the image
flags for each atom. Unwrapped means that if the atom has passed thru
a periodic boundary one or more times, the value is printed for what
the coordinate would be if it had not been wrapped back into the
periodic box. Note that these coordinates may thus be far outside the
box size stored with the snapshot.
</P>
<P>The <I>every</I> option changes the dump frequency originally specified by
the <A HREF = "dump.html">dump</A> command to a new value which must be > 0. The
dump frequency cannot be changed for the dump <I>dcd</I> style.
</P>
<P>The <I>precision</I> option only applies to the dump <I>xtc</I> style. A
specified value of N means that coordinates are stored to 1/N
nanometer accuracy, e.g. for N = 1000, the coordinates are written to
1/1000 nanometer accuracy.
</P>
<P>The <I>region</I> keyword only applies to the dump <I>custom</I> 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 <A HREF = "region.html">region</A> 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.
</P>
<P>The <I>thresh</I> keyword only applies to the dump <I>custom</I> style.
Multiple thresholds can be specified. Specifying "none" turns off
all threshold criteria. If thresholds are specified, only atoms
whose attributes meet all the threshold 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 <A HREF = "dump.html">dump custom</A>
command. Note that different attributes can be output by the dump
custom command than are used as threshold criteria by the dump_modify
command. E.g. you can output the coordinates and stress of atoms
whose energy is above some threshold.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "dump.html">dump</A>, <A HREF = "undump.html">undump</A>
</P>
<P><B>Default:</B>
</P>
<P>The option defaults are format = %d and %g for each integer or
floating point value, scale = yes, image = no, flush = yes (except for
the dump <I>xtc</I> style), unwrap = no, every = whatever it was set to via
the <A HREF = "dump.html">dump</A> command, precision = 1000, region = none, and
thresh = none.
</P>
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