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<title>compute slice command — LAMMPS 15 May 2015 version documentation</title>
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<li class="toctree-l1"><a class="reference internal" href="Section_accelerate.html">5. Accelerating LAMMPS performance</a></li>
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<div class="section" id="compute-slice-command">
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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>
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<div class="section" id="syntax">
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<h2>Syntax<a class="headerlink" href="#syntax" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>compute ID group-ID slice Nstart Nstop Nskip input1 input2 ...
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</pre></div>
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</div>
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<ul class="simple">
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<li>ID, group-ID are documented in <a class="reference internal" href="compute.html"><em>compute</em></a> command</li>
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<li>slice = style name of this compute command</li>
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<li>Nstart = starting index within input vector(s)</li>
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<li>Nstop = stopping index within input vector(s)</li>
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<li>Nskip = extract every Nskip elements from input vector(s)</li>
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<li>input = c_ID, c_ID[N], f_ID, f_ID[N]</li>
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</ul>
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<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
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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
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</pre></div>
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</div>
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</div>
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<div class="section" id="examples">
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<h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2>
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<div class="highlight-python"><div class="highlight"><pre>compute 1 all slice 1 100 10 c_msdmol[4]
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compute 1 all slice 301 400 1 c_msdmol[4]
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</pre></div>
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</div>
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</div>
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<div class="section" id="description">
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<h2>Description<a class="headerlink" href="#description" title="Permalink to this headline">¶</a></h2>
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<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
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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
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three kinds of quantities. <a class="reference internal" href="variable.html"><em>Variables</em></a> do not generate
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global vectors. The group specified with this command is ignored.</p>
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<p>The values extracted from the input vector(s) are determined by the
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<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
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element <em>Nstop</em> is reached. The extracted quantities are stored as a
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vector, which is typically shorter than the input vector.</p>
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<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
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<a class="reference internal" href="fix.html"><em>fix</em></a>.</p>
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<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>
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<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
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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 <a class="reference internal" href="Section_modify.html"><em>add them to LAMMPS</em></a>.</p>
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<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
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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.</p>
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<hr class="docutils" />
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<p><strong>Output info:</strong></p>
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<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
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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 <a class="reference internal" href="Section_howto.html#howto-15"><span>this section</span></a> for an overview of LAMMPS output
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options.</p>
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<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
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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”.</p>
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<p>The vector or array values will be in whatever <a class="reference internal" href="units.html"><em>units</em></a> the
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input quantities are in.</p>
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</div>
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<div class="section" id="restrictions">
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<h2>Restrictions<a class="headerlink" href="#restrictions" title="Permalink to this headline">¶</a></h2>
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<blockquote>
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<div>none</div></blockquote>
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</div>
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<div class="section" id="related-commands">
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<h2>Related commands<a class="headerlink" href="#related-commands" title="Permalink to this headline">¶</a></h2>
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<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>
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<p><strong>Default:</strong> none</p>
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