`dst_inputs` when g.is_blcok==True

s6juncheng · January 8, 2021, 11:52am

Thank the DGL team for creating such a great tool.

I have a question about the way to get dis_inputs, specifically this line:

dmlc/dgl/blob/8bbc84e04fe33a5459b85ad09e92b5a78325f214/python/dgl/nn/pytorch/hetero.py#L149


if mod_args is None:
    mod_args = {}
if mod_kwargs is None:
    mod_kwargs = {}
outputs = {nty : [] for nty in g.dsttypes}
if isinstance(inputs, tuple) or g.is_block:
    if isinstance(inputs, tuple):
        src_inputs, dst_inputs = inputs
    else:
        src_inputs = inputs
        dst_inputs = {k: v[:g.number_of_dst_nodes(k)] for k, v in inputs.items()}
    for stype, etype, dtype in g.canonical_etypes:
        rel_graph = g[stype, etype, dtype]
        if rel_graph.number_of_edges() == 0:
            continue
        if stype not in src_inputs or dtype not in dst_inputs:
            continue
        dstdata = self.mods[etype](
            rel_graph,
            (src_inputs[stype], dst_inputs[dtype]),

v[:g.number_of_dst_nodes(k)] is subseting the first n entries of the input feature matrix, where n=g.number_of_dst_nodes(k) being the number of dst nodes. Unless the input feature matrix is ordered in a way that the first n entries corresponding to dst nodes, I don’t really understand why we could simply subset. Are we need to do something like v[dst_nids]?

Similar logics also applies to specific layers like https://github.com/dmlc/dgl/blob/8bbc84e04fe33a5459b85ad09e92b5a78325f214/python/dgl/nn/pytorch/conv/sageconv.py#L181

I read through the code but could not figure out how. Looking forward to your answer.

BarclayII · January 11, 2021, 3:09am

Indeed they are, if the graph is a block (i.e. g.is_block is True). This property is ensured by the to_block function, which converts a graph into a bipartite graph, with destination nodes on the “output” side and the union of source and destination nodes on the “input” side.

The implementation is in C++ function ToBlock in src/graph/transform/to_bipartite.cc.

system · February 10, 2021, 3:09am

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