forked from lijiext/lammps
109 lines
3.8 KiB
Plaintext
109 lines
3.8 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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group command :h3
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[Syntax:]
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group ID style args :pre
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ID = user-defined name of the group :ulb,l
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style = {delete} or {region} or {type} or {id} or {molecule} or {subtract} or \
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{union} or {intersect} :l
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{delete} = no args
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{region} args = region-ID
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{type} or {id} or {molecule}
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args = one or more atom types, atom IDs, or molecule IDs
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args = logical value
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logical = "<" or "<=" or ">" or ">=" or "==" or "!="
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value = an atom type or atom ID or molecule ID (depending on {style})
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args = logical value1 value2
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logical = "<>"
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value1,value2 = atom types or atom IDs or molecule IDs
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(depending on {style})
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{subtract} args = two or more group IDs
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{union} args = one or more group IDs
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{intersect} args = two or more group IDs :pre
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:ule
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[Examples:]
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group edge region regstrip
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group water type 3 4
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group sub id <= 150
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group polyA molecule <> 50 250
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group boundary subtract all a2 a3
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group boundary union lower upper
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group boundary intersect upper flow
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group boundary delete :pre
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[Description:]
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Identify a collection of atoms as belonging to a group. The group ID
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can then be used in other commands such as "fix"_fix.html,
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"compute"_compute.html, "dump"_dump.html, or "velocity"_velocity.html
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to act on those atoms together.
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If the group ID already exists, the group command adds the specified
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atoms to the group.
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The {delete} style removes the named group and un-assigns all atoms
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that were assigned to that group. Since there is a restriction (see
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below) that no more than 32 groups can be defined at any time, the
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{delete} style allows you to remove groups that are no longer needed,
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so that more can be specified. You cannot delete a group if it has
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been used to define a current "fix"_fix.html or "compute"_compute.html
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or "dump"_dump.html.
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The {region} style puts all atoms in the region volume into the group.
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Note that this is a static one-time assignment. The atoms remain
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assigned (or not assigned) to the group even in they later move out of
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the region volume.
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The {type}, {id}, and {molecule} styles put all atoms with the
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specified atom types, atom IDs, or molecule IDs into the group. These
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3 styles can have their arguments specified in one of two formats.
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The 1st format is a list of values (types or IDs). For example, the
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2nd command in the examples above puts all atoms of type 3 or 4 into
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the group named {water}. The 2nd format is a {logical} followed by
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one or two values (type or ID). The 7 valid logicals are listed
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above. All the logicals except <> take a single argument. The 3rd
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example above adds all atoms with IDs from 1 to 150 to the group named
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{sub}. The logical <> means "between" and takes 2 arguments. The 4th
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example above adds all atoms belonging to molecules with IDs from 50
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to 250 (inclusive) to the group named polyA.
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The {subtract} style takes a list of two or more existing group names
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as arguments. All atoms that belong to the 1st group, but not to any
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of the other groups are added to the specified group.
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The {union} style takes a list of one or more existing group names as
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arguments. All atoms that belong to any of the listed groups are
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added to the specified group.
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The {intersect} style takes a list of two or more existing group names
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as arguments. Atoms that belong to every one of the listed groups are
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added to the specified group.
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A group with the ID {all} is predefined. All atoms belong to this
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group. This group cannot be deleted.
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[Restrictions:]
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There can be no more than 32 groups defined at one time, including
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"all".
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[Related commands:]
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"dump"_dump.html, "fix"_fix.html, "region"_region.html,
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"velocity"_velocity.html
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[Default:]
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All atoms belong to the "all" group.
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