Strongly connected components Part 1 (trimming zero in|out degree vertices)

[wu6u3]

No description provided.

[rapids-bot]

Pull requests from external contributors require approval from a rapidsai organization member with write or admin permissions before CI can begin.

[seunghwak]

thrust::distance takes (first, last) (instead of (last, first)), so this should be thrust::distance(remaining_vertices.begin(), thrust::copy_if(...))

You cannot directly pass an rmm::device_uvector object by value to the device functor from the host, so this should be like

[in_degree = raft::device_span<edge_t const>(in_degrees.data(), in_degrees.size()), out_degree = raft::device_span<edge_t const>(out_degrees.data(), out_degrees.size()), vertex_first = graph_view.local_vertex_partition_range_first()]__device__(vertex_t v) {
  auto offset = v - vertex_first;
  return in_degrees[offset] >= 1 && out_degrees[offset] >=1;
}

Note that we are encouraging to use raft::host_span and raft::device_span instead of raw pointers (see std::span https://en.cppreference.com/w/cpp/container/span if you are not familiar with the concept of span).

[seunghwak]

Finding vertices with non-zero in|out degrees and finding induced subgraph is one way to solve this problem.

Another more direct approach is to use extract_if_e.

  if (graph_view.count_self_loops(handle) > edge_t{0}) {
    auto [srcs, dsts] = extract_if_e(handle,
                                     graph_view,
                                     edge_src_dummy_property_t{}.view(),
                                     edge_dst_dummy_property_t{}.view(),
                                     is_not_self_loop_t<vertex_t>{});

    if constexpr (multi_gpu) {
      std::tie(srcs, dsts, std::ignore, std::ignore) =
        detail::shuffle_ext_vertex_pairs_to_local_gpu_by_edge_partitioning<vertex_t,
                                                                           edge_t,
                                                                           weight_t,
                                                                           int32_t>(
          handle, std::move(srcs), std::move(dsts), std::nullopt, std::nullopt);
    }

    std::tie(*modified_graph, std::ignore, std::ignore, renumber_map) =
      create_graph_from_edgelist<vertex_t, edge_t, weight_t, int32_t, false, multi_gpu>(
        handle,
        std::nullopt,
        std::move(srcs),
        std::move(dsts),
        std::nullopt,
        std::nullopt,
        cugraph::graph_properties_t{true, graph_view.is_multigraph()},
        true);

    modified_graph_view = (*modified_graph).view();
  }

https://github.com/rapidsai/cugraph/blob/branch-23.04/cpp/src/community/triangle_count_impl.cuh#L201

Here, instead of passing dummy property views, you need to pass in_degrees and out_degrees.

See

    edge_src_property_t<decltype(cur_graph_view), uint8_t> edge_src_in_two_cores(handle,
                                                                                 cur_graph_view);
    edge_dst_property_t<decltype(cur_graph_view), uint8_t> edge_dst_in_two_cores(handle,
                                                                                 cur_graph_view);

https://github.com/rapidsai/cugraph/blob/branch-23.04/cpp/src/community/triangle_count_impl.cuh#L246

and

    update_edge_src_property(
      handle, cur_graph_view, in_two_core_flags.begin(), edge_src_in_two_cores);
    update_edge_dst_property(
      handle, cur_graph_view, in_two_core_flags.begin(), edge_dst_in_two_cores);

https://github.com/rapidsai/cugraph/blob/branch-23.04/cpp/src/community/triangle_count_impl.cuh#L257

and

                                     edge_src_in_two_cores.view(),
                                     edge_dst_in_two_cores.view(),

https://github.com/rapidsai/cugraph/blob/branch-23.04/cpp/src/community/triangle_count_impl.cuh#L263

to figure out how to do this.

Let me know if you have additional questions.

[seunghwak]

#3325 is replacing this PR.