forked from lijiext/lammps
115 lines
4.7 KiB
HTML
115 lines
4.7 KiB
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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>
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<HR>
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<H3>dump_modify command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>dump_modify dump-ID keyword args ...
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</PRE>
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<UL><LI>dump-ID = ID of dump to modify
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<LI>one or more keyword/arg pairs may be appended
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<LI>keyword = <I>format</I> or <I>scale</I> or <I>image</I> or <I>header</I> or <I>flush</I> or <I>region</I> or <I>thresh</I>
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<PRE> <I>format</I> arg = C-style format string for one line of output
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<I>scale</I> arg = <I>yes</I> or <I>no</I>
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<I>image</I> arg = <I>yes</I> or <I>no</I>
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<I>flush</I> arg = <I>yes</I> or <I>no</I>
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<I>every</I> arg = N
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N = dump every this many timesteps
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<I>region</I> arg = region-ID or "none"
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<I>thresh</I> args = attribute operation value
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attribute = same attributes (x,fy,eng,sxx,etc) used by dump custom style
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operation = < or <= or > or >= or = or <>
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value = numeric value to compare to
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these 3 args can be replaced by the word "none" to turn off threshholding
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</PRE>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>dump_modify 1 format "%d %d %20.15g %g %g" scale yes
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dump_modify myDump image yes scale no flush yes
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dump_modify 1 region mySphere thresh x < 0.0 thresh energy >= 3.2
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Modify the parameters of a previously defined dump command. Not all
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parameters are relevant to all dump styles.
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</P>
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<P>The text-based dump styles have a default C-style format string which
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simply specifies %d for integers and %g for real values. The <I>format</I>
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keyword can be used to override the default with a new C-style format
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string. Do not include a trailing "\n" newline character in the
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format string. This option has no effect on the <I>dcd</I> and <I>xtc</I> dump
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styles since they write binary files.
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</P>
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<P>The <I>scale</I> and <I>image</I> keywords apply only to the dump <I>atom</I> style.
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A scale value of <I>yes</I> means atom coords are written in normalized
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units from 0.0 to 1.0 in each box dimension. A value of <I>no</I> means
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they are written in absolute distance units (e.g. Angstroms or sigma).
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If the image value is <I>yes</I>, 3 flags are appended to each atom's
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coords which are the absolute box image of the atom in each dimension.
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For example, an x image flag of -2 with a normalized coord of 0.5
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means the atom is in the center of the box, but has passed thru the
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box boundary 2 times and is really 2 box lengths to the left of its
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current coordinate. Note that for dump style <I>custom</I> these values
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can be printed in the dump file by using the appropriate atom
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attributes in the dump command itself.
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</P>
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<P>The <I>flush</I> option determines whether a flush operation in invoked
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after a dump snapshot is written to the dump file. A flush insures
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the output in that file is current (no buffering by the OS), even if
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LAMMPS halts before the simulation completes. Flushes cannot be
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performed with dump style <I>xtc</I>.
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</P>
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<P>The <I>every</I> option changes the dump frequency originally specified by
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the <A HREF = "dump.html">dump</A> command to a new value which must be > 0. The
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dump frequency cannot be changed for the dump <I>dcd</I> style.
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</P>
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<P>The <I>region</I> keyword only applies to the dump <I>custom</I> style. If
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specified, only atoms in the region will be written to the dump file.
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Only one region can be applied as a filter (the last one specified).
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See the <A HREF = "region.html">region</A> command for more details. Note that a
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region can be defined as the "inside" or "outside" of a geometric
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shape, and it can be the "union" or "intersection" of a series of
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simpler regions.
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</P>
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<P>The <I>thresh</I> keyword only applies to the dump <I>custom</I> style.
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Multiple threshholds can be specified. Specifying "none" turns off
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all threshhold criteria. If theshholds are specified, only atoms
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whose attributes meet all the threshhold criteria are written to the
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dump file. The possible attributes that can be tested for are the
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same as those that can be specified in the <A HREF = "dump.html">dump custom</A>
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command. Note that different attributes can be output by the dump
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custom command than are used as threshhold criteria by the dump_modify
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command. E.g. you can output the coordinates and stress of atoms
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whose energy is above some thresshold.
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</P>
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<P><B>Restrictions:</B> none
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "dump.html">dump</A>, <A HREF = "undump.html">undump</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>The option defaults are format = %d and %g for each integer or
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floating point value, scale = yes, image = no, flush = yes (except for
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dump <I>xtc</I> style), region = none, and thresh = none.
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</P>
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</HTML>
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