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< title > compute slice command — LAMMPS 15 May 2015 version documentation< / title >
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< li > compute slice command< / li >
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< a href = "http://lammps.sandia.gov" > Website< / a >
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< span id = "index-0" > < / span > < h1 > compute slice command< a class = "headerlink" href = "#compute-slice-command" title = "Permalink to this headline" > ¶< / a > < / h1 >
< div class = "section" id = "syntax" >
< h2 > Syntax< a class = "headerlink" href = "#syntax" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > compute ID group-ID slice Nstart Nstop Nskip input1 input2 ...
< / pre > < / div >
< / div >
< ul class = "simple" >
< li > ID, group-ID are documented in < a class = "reference internal" href = "compute.html" > < em > compute< / em > < / a > command< / li >
< li > slice = style name of this compute command< / li >
< li > Nstart = starting index within input vector(s)< / li >
< li > Nstop = stopping index within input vector(s)< / li >
< li > Nskip = extract every Nskip elements from input vector(s)< / li >
< li > input = c_ID, c_ID[N], f_ID, f_ID[N]< / li >
< / ul >
< div class = "highlight-python" > < div class = "highlight" > < pre > 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
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 > < / div >
< / div >
< / div >
< div class = "section" id = "examples" >
< h2 > Examples< a class = "headerlink" href = "#examples" title = "Permalink to this headline" > ¶< / a > < / h2 >
< div class = "highlight-python" > < div class = "highlight" > < pre > compute 1 all slice 1 100 10 c_msdmol[4]
compute 1 all slice 301 400 1 c_msdmol[4]
< / pre > < / div >
< / div >
< / div >
< div class = "section" id = "description" >
< h2 > Description< a class = "headerlink" href = "#description" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > 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
quantities; they cannot be per-atom or local quantities.
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< a class = "reference internal" href = "compute.html" > < em > Computes< / em > < / a > and < a class = "reference internal" href = "fix.html" > < em > fixes< / em > < / a > may generate any of the
three kinds of quantities. < a class = "reference internal" href = "variable.html" > < em > Variables< / em > < / a > do not generate
global vectors. The group specified with this command is ignored.< / p >
< p > The values extracted from the input vector(s) are determined by the
< em > Nstart< / em > , < em > Nstop< / em > , and < em > Nskip< / em > 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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< em > Nstart< / em > , every Mth element is extracted, where M = < em > Nskip< / em > , until
element < em > Nstop< / em > is reached. The extracted quantities are stored as a
vector, which is typically shorter than the input vector.< / p >
< p > 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 < a class = "reference internal" href = "compute.html" > < em > compute< / em > < / a > or
< a class = "reference internal" href = "fix.html" > < em > fix< / em > < / a > .< / p >
< p > If an input value begins with “ < a href = "#id1" > < span class = "problematic" id = "id2" > c_< / span > < / a > ” , 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 < a class = "reference internal" href = "compute.html" > < em > compute< / em > < / a > 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 < a class = "reference internal" href = "Section_modify.html" > < em > add them to LAMMPS< / em > < / a > .< / p >
< p > If a value begins with “ < a href = "#id3" > < span class = "problematic" id = "id4" > f_< / span > < / a > ” , 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 < a class = "reference internal" href = "fix.html" > < em > fix< / em > < / a > doc page for
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details. Note that some fixes only produce their values on certain
timesteps, which must be compatible with when compute slice references
the values, else an error results. If no bracketed integer is
appended, the vector calculated by the fix is used. If a bracketed
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 < a class = "reference internal" href = "Section_modify.html" > < em > add them to LAMMPS< / em > < / a > .< / p >
< p > 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
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.< / p >
< hr class = "docutils" / >
< p > < strong > Output info:< / strong > < / p >
< p > 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
inputs. The length of the vector or the number of rows in the array
is equal to the number of values extracted from each input vector.
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 < a class = "reference internal" href = "Section_howto.html#howto-15" > < span > this section< / span > < / a > for an overview of LAMMPS output
options.< / p >
< p > 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
to this compute. If there is a single input vector of intensive
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
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” .< / p >
< p > The vector or array values will be in whatever < a class = "reference internal" href = "units.html" > < em > units< / em > < / a > the
input quantities are in.< / p >
< / div >
< div class = "section" id = "restrictions" >
< h2 > Restrictions< a class = "headerlink" href = "#restrictions" title = "Permalink to this headline" > ¶< / a > < / h2 >
< blockquote >
< div > none< / div > < / blockquote >
< / div >
< div class = "section" id = "related-commands" >
< h2 > Related commands< a class = "headerlink" href = "#related-commands" title = "Permalink to this headline" > ¶< / a > < / h2 >
< p > < a class = "reference internal" href = "compute.html" > < em > compute< / em > < / a > , < a class = "reference internal" href = "fix.html" > < em > fix< / em > < / a > , < a class = "reference internal" href = "compute_reduce.html" > < em > compute reduce< / em > < / a > < / p >
< p > < strong > Default:< / strong > none< / p >
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