Add support in C API for handling unweighted graphs in algorithms tha…

…t expect weights (#3513)

Closes #3499 

Some of our C++ algorithms require a graph to be weighted.  The python layer will add "fake" edge weights of 1 to every edge in order to call these algorithms.  This adds a persisted constant value for every edge that will continue to exist for the life span of the python graph object, even though it is only necessary for a handful of algorithms.

This PR addresses these concerns.

Many of the C++ algorithms already actually support the graph not having weights.  A few should support it and had bugs that were corrected (induced subgraph, k-core, egonet).  A few can easily support it but did not (legacy spectral algorithms).

The Louvain and Leiden algorithms need to have a weighted graph because they will coarsen the weights as the graph is coarsened, and the weights will eventually not be one while the algorithm is running.  These require a slightly different approach.

This PR also added C API tests for unweighted graphs for these algorithms.

Authors:
  - Chuck Hastings (https://github.com/ChuckHastings)
  - Brad Rees (https://github.com/BradReesWork)

Approvers:
  - Seunghwa Kang (https://github.com/seunghwak)

URL: #3513

cpp/CMakeLists.txt

@@ -404,7 +404,8 @@ add_library(cugraph_c
         src/c_api/capi_helper.cu
         src/c_api/legacy_spectral.cpp
         src/c_api/legacy_ecg.cpp
-        src/c_api/graph_helper.cu
+        src/c_api/graph_helper_sg.cu
+        src/c_api/graph_helper_mg.cu
         src/c_api/graph_generators.cpp
         src/c_api/induced_subgraph_result.cpp
         src/c_api/hits.cpp

cpp/src/c_api/core_result.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, NVIDIA CORPORATION.
+ * Copyright (c) 2022-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -95,8 +95,10 @@ cugraph_type_erased_device_array_view_t* cugraph_k_core_result_get_weights(
   cugraph_k_core_result_t* result)
 {
   auto internal_pointer = reinterpret_cast<cugraph::c_api::cugraph_k_core_result_t*>(result);
-  return reinterpret_cast<cugraph_type_erased_device_array_view_t*>(
-    internal_pointer->weights_->view());
+  return (internal_pointer->weights_ == nullptr)
+           ? NULL
+           : reinterpret_cast<cugraph_type_erased_device_array_view_t*>(
+               internal_pointer->weights_->view());
 }
 
 void cugraph_k_core_result_free(cugraph_k_core_result_t* result)

cpp/src/c_api/graph_helper.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, NVIDIA CORPORATION.
+ * Copyright (c) 2022-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -26,5 +26,10 @@ rmm::device_uvector<vertex_t> expand_sparse_offsets(raft::device_span<edge_t con
                                                     vertex_t base_vertex_id,
                                                     rmm::cuda_stream_view const& stream);
 
+template <typename GraphViewType, typename T>
+edge_property_t<GraphViewType, T> create_constant_edge_property(raft::handle_t const& handle,
+                                                                GraphViewType const& graph_view,
+                                                                T constant_value);
+
 }  // namespace c_api
 }  // namespace cugraph

cpp/src/c_api/graph_helper_impl.cuh

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) 2022-2023, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#pragma once
+
+#include <prims/fill_edge_property.cuh>
+#include <structure/detail/structure_utils.cuh>
+
+namespace cugraph {
+namespace c_api {
+
+template <typename vertex_t, typename edge_t>
+rmm::device_uvector<vertex_t> expand_sparse_offsets(raft::device_span<edge_t const> offsets,
+                                                    vertex_t base_vertex_id,
+                                                    rmm::cuda_stream_view const& stream)
+{
+  return cugraph::detail::expand_sparse_offsets(offsets, base_vertex_id, stream);
+}
+
+template <typename GraphViewType, typename T>
+edge_property_t<GraphViewType, T> create_constant_edge_property(raft::handle_t const& handle,
+                                                                GraphViewType const& graph_view,
+                                                                T constant_value)
+{
+  edge_property_t<GraphViewType, T> edge_property(handle, graph_view);
+
+  cugraph::fill_edge_property(handle, graph_view, constant_value, edge_property);
+
+  return edge_property;
+}
+
+}  // namespace c_api
+}  // namespace cugraph

cpp/src/c_api/graph_helper_mg.cu

@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2023, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <c_api/graph_helper_impl.cuh>
+
+namespace cugraph {
+namespace c_api {
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, false, true>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int32_t, false, true> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, false, true>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int64_t, false, true> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, false, true>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int64_t, int64_t, false, true> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, true, true>, float>
+create_constant_edge_property(raft::handle_t const& handle,
+                              cugraph::graph_view_t<int32_t, int32_t, true, true> const& graph_view,
+                              float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, true, true>, float>
+create_constant_edge_property(raft::handle_t const& handle,
+                              cugraph::graph_view_t<int32_t, int64_t, true, true> const& graph_view,
+                              float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, true, true>, float>
+create_constant_edge_property(raft::handle_t const& handle,
+                              cugraph::graph_view_t<int64_t, int64_t, true, true> const& graph_view,
+                              float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, false, true>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int32_t, false, true> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, false, true>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int64_t, false, true> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, false, true>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int64_t, int64_t, false, true> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, true, true>, double>
+create_constant_edge_property(raft::handle_t const& handle,
+                              cugraph::graph_view_t<int32_t, int32_t, true, true> const& graph_view,
+                              double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, true, true>, double>
+create_constant_edge_property(raft::handle_t const& handle,
+                              cugraph::graph_view_t<int32_t, int64_t, true, true> const& graph_view,
+                              double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, true, true>, double>
+create_constant_edge_property(raft::handle_t const& handle,
+                              cugraph::graph_view_t<int64_t, int64_t, true, true> const& graph_view,
+                              double constant_value);
+
+}  // namespace c_api
+}  // namespace cugraph

cpp/src/c_api/graph_helper_sg.cu

@@ -0,0 +1,118 @@
+/*
+ * Copyright (c) 2022-2023, NVIDIA CORPORATION.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <c_api/graph_helper_impl.cuh>
+
+namespace cugraph {
+namespace c_api {
+
+template rmm::device_uvector<int32_t> expand_sparse_offsets(
+  raft::device_span<int32_t const> offsets,
+  int32_t base_vertex_id,
+  rmm::cuda_stream_view const& stream);
+
+template rmm::device_uvector<int32_t> expand_sparse_offsets(
+  raft::device_span<int64_t const> offsets,
+  int32_t base_vertex_id,
+  rmm::cuda_stream_view const& stream);
+
+template rmm::device_uvector<int64_t> expand_sparse_offsets(
+  raft::device_span<int64_t const> offsets,
+  int64_t base_vertex_id,
+  rmm::cuda_stream_view const& stream);
+
+template rmm::device_uvector<int32_t> expand_sparse_offsets(raft::device_span<size_t const> offsets,
+                                                            int32_t base_vertex_id,
+                                                            rmm::cuda_stream_view const& stream);
+
+template rmm::device_uvector<int64_t> expand_sparse_offsets(raft::device_span<size_t const> offsets,
+                                                            int64_t base_vertex_id,
+                                                            rmm::cuda_stream_view const& stream);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, false, false>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int32_t, false, false> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, false, false>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int64_t, false, false> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, false, false>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int64_t, int64_t, false, false> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, true, false>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int32_t, true, false> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, true, false>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int64_t, true, false> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, true, false>, float>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int64_t, int64_t, true, false> const& graph_view,
+  float constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, false, false>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int32_t, false, false> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, false, false>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int64_t, false, false> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, false, false>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int64_t, int64_t, false, false> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int32_t, true, false>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int32_t, true, false> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int32_t, int64_t, true, false>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int32_t, int64_t, true, false> const& graph_view,
+  double constant_value);
+
+template edge_property_t<cugraph::graph_view_t<int64_t, int64_t, true, false>, double>
+create_constant_edge_property(
+  raft::handle_t const& handle,
+  cugraph::graph_view_t<int64_t, int64_t, true, false> const& graph_view,
+  double constant_value);
+
+}  // namespace c_api
+}  // namespace cugraph

cpp/src/c_api/induced_subgraph_result.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2022, NVIDIA CORPORATION.
+ * Copyright (c) 2022-2023, NVIDIA CORPORATION.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -39,7 +39,10 @@ extern "C" cugraph_type_erased_device_array_view_t* cugraph_induced_subgraph_get
 {
   auto internal_pointer =
     reinterpret_cast<cugraph::c_api::cugraph_induced_subgraph_result_t*>(induced_subgraph);
-  return reinterpret_cast<cugraph_type_erased_device_array_view_t*>(internal_pointer->wgt_->view());
+  return (internal_pointer->wgt_ == nullptr)
+           ? NULL
+           : reinterpret_cast<cugraph_type_erased_device_array_view_t*>(
+               internal_pointer->wgt_->view());
 }
 
 extern "C" cugraph_type_erased_device_array_view_t* cugraph_induced_subgraph_get_subgraph_offsets(