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<p>
A periodic dump is a parallelepiped whose edges are the columns of H.
Cartesian coordinates fold to fractional coordinates <code>s = Hinv (r -
origin)</code>, wrap each component into the central image, then map back
<code>r = H s</code>. Squared distance is <code>|H wrap(Hinv (q - p))|^2</code>.
</p>
<p>
Orthorhombic boxes are the diagonal case. Each axis wraps on its own
length. The batched kernel hoists one reciprocal per axis and wraps
precomputed differences, the same arithmetic as a Highway
<code>BatchPeriodicDistSq</code> loop. The signed wrap keeps <code>-L/2</code> and maps
<code>+L/2</code> onto <code>-L/2</code>, matching dump <code>relDist</code>.
</p>
<section id="outline-container-orgc2d6f0e" class="outline-2">
<h2 id="orgc2d6f0e">Dump bounds are not H</h2>
<div class="outline-text-2" id="text-orgc2d6f0e">
<p>
LAMMPS ITEM BOX BOUNDS stores bound spans plus tilt <code>xy, xz, yz</code>.
<code>Cell::from_lammps_bounds</code> recovers the restricted-triclinic H and
origin:
</p>
<div class="org-src-container">
<pre class="src src-text">xlo_bound = xlo + min(0, xy, xz, xy+xz)
</pre>
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<p>
A CON header may already hold the 3x3 lattice, or lengths and angles
in the crystallographic convention. ASE and vesin pass rows <code>(a, b,
c)</code>.
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<section id="outline-container-org635c4e0" class="outline-2">
<h2 id="org635c4e0">vesin images</h2>
<div class="outline-text-2" id="text-org635c4e0">
<p>
vesin enumerates periodic images. A particle can appear as its own
neighbour through an image, and one neighbour can arrive through
several images. <code>reduce_pairs</code> keeps each ordered pair once and drops
the self image.
</p>
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<section id="outline-container-org1f6f2dd" class="outline-2">
<h2 id="org1f6f2dd">Consumers</h2>
<div class="outline-text-2" id="text-org1f6f2dd">
<p>
linkcell re-exports <code>minimage::Cell</code> for the fold and the lattice
shift. d-SEAMS calls the C ABI from <code>lammpsBoxToLcCell</code>,
<code>periodicDistSq</code> / <code>relDist</code>, the ortho batch kernel, and the vesin
pair collapse.
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