NodeFormer: A Scalable Graph Structure Learning Transformer for Node
  Classification
Qitian Wu Wentao Zhao Zenan Li David Wipf Junchi Yan
Graph neural networks have been extensively studied for learning with
inter-connected data. Despite this, recent evidence has revealed GNNs'
deficiencies related to over-squashing, heterophily, handling long-range
dependencies, edge incompleteness and particularly, the absence of graphs
altogether. While a plausible solution is to learn new adaptive topology for
message passing, issues concerning quadratic complexity hinder simultaneous
guarantees for scalability and precision in large networks. In this paper, we
introduce a novel all-pair message passing scheme for efficiently propagating
node signals between arbitrary nodes, as an important building block for a
pioneering Transformer-style network for node classification on large graphs,
dubbed as \textsc{NodeFormer}. Specifically, the efficient computation is
enabled by a kernerlized Gumbel-Softmax operator that reduces the algorithmic
complexity to linearity w.r.t. node numbers for learning latent graph
structures from large, potentially fully-connected graphs in a differentiable
manner. We also provide accompanying theory as justification for our design.
Extensive experiments demonstrate the promising efficacy of the method in
various tasks including node classification on graphs (with up to 2M nodes) and
graph-enhanced applications (e.g., image classification) where input graphs are
missing.