forked from lijiext/lammps
113 lines
4.7 KiB
Plaintext
113 lines
4.7 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 slice command :h3
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[Syntax:]
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compute ID group-ID slice Nstart Nstop Nskip input1 input2 ... :pre
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ID, group-ID are documented in "compute"_compute.html command :ulb,l
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slice = style name of this compute command :l
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Nstart = starting index within input vector(s) :l
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Nstop = stopping index within input vector(s) :l
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Nskip = extract every Nskip elements from input vector(s) :l
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input = c_ID, c_ID\[N\], f_ID, f_ID\[N\] :l
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c_ID = global vector calculated by a compute with ID
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c_ID\[I\] = Ith column of global array calculated by a compute with ID
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f_ID = global vector calculated by a fix with ID
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f_ID\[I\] = Ith column of global array calculated by a fix with ID :pre
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:ule
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[Examples:]
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compute 1 all slice 1 100 10 c_msdmol\[4\]
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compute 1 all slice 301 400 1 c_msdmol\[4\] :pre
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[Description:]
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Define a calculation that "slices" one or more vector inputs into
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smaller vectors, one per listed input. The inputs can be global
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quantities; they cannot be per-atom or local quantities.
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"Computes"_compute.html and "fixes"_fix.html may generate any of the
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three kinds of quantities. "Variables"_variable.html do not generate
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global vectors. The group specified with this command is ignored.
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The values extracted from the input vector(s) are determined by the
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{Nstart}, {Nstop}, and {Nskip} parameters. The elements of an input
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vector of length N are indexed from 1 to N. Starting at element
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{Nstart}, every Mth element is extracted, where M = {Nskip}, until
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element {Nstop} is reached. The extracted quantities are stored as a
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vector, which is typically shorter than the input vector.
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Each listed input is operated on independently to produce one output
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vector. Each listed input must be a global vector or column of a
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global array calculated by another "compute"_compute.html or
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"fix"_fix.html.
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If an input value begins with "c_", a compute ID must follow which has
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been previously defined in the input script and which generates a
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global vector or array. See the individual "compute"_compute.html doc
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page for details. If no bracketed integer is appended, the vector
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calculated by the compute is used. If a bracketed integer is
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appended, the Ith column of the array calculated by the compute is
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used. Users can also write code for their own compute styles and "add
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them to LAMMPS"_Section_modify.html.
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If a value begins with "f_", a fix ID must follow which has been
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previously defined in the input script and which generates a global
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vector or array. See the individual "fix"_fix.html doc page for
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details. Note that some fixes only produce their values on certain
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timesteps, which must be compatible with when compute slice references
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the values, else an error results. If no bracketed integer is
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appended, the vector calculated by the fix is used. If a bracketed
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integer is appended, the Ith column of the array calculated by the fix
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is used. Users can also write code for their own fix style and "add
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them to LAMMPS"_Section_modify.html.
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If a single input is specified this compute produces a global vector,
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even if the length of the vector is 1. If multiple inputs are
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specified, then a global array of values is produced, with the number
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of columns equal to the number of inputs specified.
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:line
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[Output info:]
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This compute calculates a global vector if a single input value is
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specified or a global array with N columns where N is the number of
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inputs. The length of the vector or the number of rows in the array
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is equal to the number of values extracted from each input vector.
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These values can be used by any command that uses global vector or
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array values from a compute as input. See "this
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section"_Section_howto.html#howto_15 for an overview of LAMMPS output
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options.
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The vector or array values calculated by this compute are simply
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copies of values generated by computes or fixes that are input vectors
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to this compute. If there is a single input vector of intensive
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and/or extensive values, then each value in the vector of values
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calculated by this compute will be "intensive" or "extensive",
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depending on the corresponding input value. If there are multiple
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input vectors, and all the values in them are intensive, then the
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array values calculated by this compute are "intensive". If there are
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multiple input vectors, and any value in them is extensive, then the
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array values calculated by this compute are "extensive".
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The vector or array values will be in whatever "units"_units.html the
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input quantities are in.
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[Restrictions:] none
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[Related commands:]
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"compute"_compute.html, "fix"_fix.html, "compute
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reduce"_compute_reduce.html
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[Default:] none
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