Hierarchical Representation Learning in Graph Neural Networks with Node Decimation Pooling
This addresses the need for efficient hierarchical representation learning in GNNs, offering an incremental improvement over existing pooling methods.
The paper tackles the problem of building deep graph neural networks (GNNs) by proposing Node Decimation Pooling (NDP), a pooling operator that generates coarser graphs while preserving topology, and it shows that NDP is more efficient than state-of-the-art operators while achieving competitive performance on graph classification tasks.
In graph neural networks (GNNs), pooling operators compute local summaries of input graphs to capture their global properties, and they are fundamental for building deep GNNs that learn hierarchical representations. In this work, we propose the Node Decimation Pooling (NDP), a pooling operator for GNNs that generates coarser graphs while preserving the overall graph topology. During training, the GNN learns new node representations and fits them to a pyramid of coarsened graphs, which is computed offline in a pre-processing stage. NDP consists of three steps. First, a node decimation procedure selects the nodes belonging to one side of the partition identified by a spectral algorithm that approximates the \maxcut{} solution. Afterwards, the selected nodes are connected with Kron reduction to form the coarsened graph. Finally, since the resulting graph is very dense, we apply a sparsification procedure that prunes the adjacency matrix of the coarsened graph to reduce the computational cost in the GNN. Notably, we show that it is possible to remove many edges without significantly altering the graph structure. Experimental results show that NDP is more efficient compared to state-of-the-art graph pooling operators while reaching, at the same time, competitive performance on a significant variety of graph classification tasks.