mirror of https://github.com/lammps/lammps.git
89 lines
3.5 KiB
Plaintext
89 lines
3.5 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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compute sum command :h3
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[Syntax:]
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compute ID group-ID sum value1 value2 ... :pre
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ID, group-ID are documented in "compute"_compute.html command :ulb,l
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sum = style name of this compute command :l
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one or more values can be listed :l
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value = x, y, z, vx, vy, vz, fx, fy, fz, c_ID, c_ID\[N\], f_ID, f_ID\[N\], v_name :l
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x,y,z,vx,vy,vz,fx,fy,fz = atom attribute (position, velocity, force component)
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c_ID = per-atom scalar value calculated by a compute with ID
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c_ID\[N\] = Nth component of per-atom vector calculated by a compute with ID
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f_ID = per-atom scalar value calculated by a fix with ID
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f_ID\[N\] = Nth component of per-atom vector calculated by a fix with ID
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v_name = per-atom value calculated by an atom-style variable with name :pre
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:ule
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[Examples:]
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compute 1 all sum c_force
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compute 2 all sum c_press[2] f_ave v_myKE :pre
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[Description:]
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Define a calculation that sums the results of one or more per-atom
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quantities across all atoms in the group to yield a global scalar or
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vector quantity. The resulting value(s) can be accessed by any
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command that uses global computes, e.g. the "thermo
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custom"_therml_style.html command or "fix ave/time"_fix_ave_time.html
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command or by a "variable"_variable.html command. See "this
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section"_Section_howto.html#4_15 of the documentation for an overview
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of output options.
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Each listed value is summed independently. The group specified with
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the command means only atoms within the group contribute to the sum.
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Note that the value that produces the per-atom quantities may define
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its own group which affects the values it returns. For example, if a
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per-atom compute is used as a value, it will generate values of 0.0
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for atoms that are not in the group specified for that compute.
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Each listed value can be an atom attribute (position, velocity, force
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component) or can be the result of a "compute"_compute.html or
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"fix"_fix.html or the evaluation of an atom-style
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"variable"_variable.html. In the latter cases, the compute, fix, or
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variable must produce a per-atom quantity, not a global quantity.
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"Computes"_compute.html that produce per-atom quantities are those
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which have the word {atom} in their style name. See the doc pages for
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individual "fixes"_fix.html to determine which ones produce per-atom
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quantities. "Variables"_variable.html of style {atom} are the only
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ones that can be used with this compute since all other variable
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styles produce global quantities.
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If a single value is specified this compute produces a global scalar
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value. If multiple values are specified, this compute produces a
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vector of global values, the length of which is equal to the
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number of values specified.
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The value(s) produced by this compute are all "extensive", meaning
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their value scales linearly with the number of atoms involved. If
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normalized values are desired, this compute can be accessed by the
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"thermo_style custom"_thermo_style.html command with "thermo_modify
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norm yes"_thermo_modify.html set as an option. Or it can be accessed
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by a "variable"_variable.html that divides by the appropriate atom
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count.
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[Output info:]
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The scalar and vector values calculated by this compute are
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"extensive", meaning they scale with the number of atoms in the
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simulation.
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[Restrictions:] none
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[Related commands:]
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"compute"_compute.html, "fix"_fix.html, "variable"_variable.html
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[Default:] none
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