<p><a href="https://pytorch-geometric.readthedocs.io/en/latest/modules/nn.html#torch_geometric.nn.conv.GATConv" rel="nofollow noreferrer">That documentation page</a> includes a link to an <a href="https://arxiv.org/pdf/1710.10903.pdf" rel="nofollow noreferrer">arxiv paper</a> that includes the following (bottom of page three)...</p>
<blockquote>
<p><a href="https://i.stack.imgur.com/hpg0n.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hpg0n.png" alt="enter image description here" /></a>
where <a href="https://i.stack.imgur.com/nWLtt.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nWLtt.png" alt="enter image description here" /></a> represents transposition and || is the concatenation operation.</p>
</blockquote>
<p>So yes, || is the concatenation operator.</p>
What does a single "||" mean in pytorch-geometric documents?
<p>For example the &quot;||&quot; (\Vert) in <a href="https://pytorch-geometric.readthedocs.io/en/latest/modules/nn.html#torch_geometric.nn.conv.GATConv" rel="nofollow noreferrer">https://pytorch-geometric.readthedocs.io/en/latest/modules/nn.html#torch_geometric.nn.conv.GATConv</a></p>