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‎README.md

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# Graph Library Proposal for the C++ Standard
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[![codecov](https://codecov.io/github/stdgraph/graph-v2/branch/master/graph/badge.svg?token=49LGWDN0U1)](https://codecov.io/github/stdgraph/graph-v2) [![MacOS](https://github.com/stdgraph/graph-v2/actions/workflows/macos.yml/badge.svg)](https://github.com/stdgraph/graph-v2/actions/workflows/macos.yml) [![Ubuntu](https://github.com/stdgraph/graph-v2/actions/workflows/ubuntu.yml/badge.svg)](https://github.com/stdgraph/graph-v2/actions/workflows/ubuntu.yml) [![Windows](https://github.com/stdgraph/graph-v2/actions/workflows/windows.yml/badge.svg)](https://github.com/stdgraph/graph-v2/actions/workflows/windows.yml) [![Documentation](https://github.com/stdgraph/graph-v2/actions/workflows/pages.yml/badge.svg)](https://github.com/stdgraph/graph-v2/actions/workflows/pages.yml)
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> This library is in the alpha stage that may include significant changes to the interface. It is not recommended for general use.
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> This library is in the **alpha stage** that may include significant changes to the interface. It is not
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> recommended for general use.
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> A **breaking change** in the near future will introduce a new concept of identifier for vertices and edges,
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> similar to the descriptor concept in the Boost Graph Library. It will replace the existing id and references
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> in the API and will allow for more flexibility in the design as well as reducing the number of concepts and
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> functions. Most functions and views will be affected. *Phil - September 2024*.
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## Overview
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This library designed to provide a useful set of algorithms, views and container(s) for graphs. It also defines
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a core Graph Container Interface that provide the basis of interacting with an abstract adjacency list graph, and
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to provide easy integration with external adjacency list graphs.
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- bi-partite and n-partite graphs are under investigation.
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- Hyper-graphs are outside the scope of this project.
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- Comments and questions are welcome and can be directed to GitHub [discussions](https://github.com/stdgraph/graph-v2/discussions) or [issues](https://github.com/stdgraph/graph-v2/issues).
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- Comments and questions are welcome and can be directed to GitHub [discussions](https://github.com/stdgraph/graph-v2/discussions)
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or [issues](https://github.com/stdgraph/graph-v2/issues).
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### Purpose
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This prototype library is an implementation of the proposed Graph Library for ISO Standard C++ as described in P1709.
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This prototype library is an implementation of the proposed Graph Library for ISO Standard C++.
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It has gone through major revisions since it was first introduced in 2019. While we are comfortable of the core design, there is
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still plenty of activity being done and refinements made in its design and implementation. Experimenting with this library is
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encouraged, keeping in mind that breaking changes are expected.
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3. Define useful concepts and traits that can be used by algorithms to describe their requirements.
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4. Support views for graph traversal commonly used by algorithms.
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5. Support optional, user-defined value_types for an edge, vertex and graph.
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5. Easy integration of existing graph containers.
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6. Have an open design to allow for extensions in the future:
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1. Support for partite (partitioned) graphs. This requires extending (changing?) the Graph Container Interface.
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This is under investigation.
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2. Support the incoming edges on a vertex (e.g. bidirectional graphs).
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3. Investigate features that might make the Interface useful outside P1709, such as sparse vertex_ids.
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This can help validate the existing design and guide decisions for the future.
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6. Allow the use of standard containers to define simple graphs.
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7. Easy integration of existing graph data structures.
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8. Have an open design to allow for extensions in the future:
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1. Support the incoming edges on a vertex (e.g. bidirectional graphs).
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2. Support sparse vertex_ids stored in bi-directional ranges (e.g. `map` and `unordered_map`).
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## Getting Started
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This is being actively developed with the latest releases of MSVC (VS2022) on Windows and gcc (11) on Linux/MacOS.
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This is being actively developed with the latest releases of MSVC (VS2022) on Windows and gcc (13) on Linux/MacOS.
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Other releases or compilers may or may not work.
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### Prerequesites
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- C++20 compliant compiler that fully supports concepts and ranges.
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- CMake 20 or later (for CMake Presets)
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- C\+\+20 compliant compiler that fully supports concepts and ranges. (C\+\+23 is required for building the benchmarks.)
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- CMake 26 or later (for CMake Presets)
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### Quick Start Guide (Linux, WSL, MacOS)
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```bash
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See https://docs.microsoft.com/en-us/cpp/build/cmake-presets-vs?view=msvc-170 for configuring Microsoft tools.
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## Description
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In the following tables, P1709 identifies that the feature is in the P1709 proposal. A value of "TBD" indicates that it
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is being considered, subject to the size of the proposal and other priorities.
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### Graph Algorithms
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| Algorithm | P1709 | Status |
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| :-------------------------------| :---- | :-------------------------------------------------------------------------------|
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| Dijkstra Shortest Paths | Yes | dijkstra_clrs: needs review |
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| Bellman-Ford Shortest Paths | Yes | needs implementation |
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| Connected Components | Yes | needs implementation |
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| Strongly Connected Components | Yes | needs implementation |
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| Bi-Connected Components | Yes | needs implementation |
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| Articulation Points | Yes | needs implementation |
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| Minimum Spanning Tree | Yes | needs implementation |
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| Page Rank | TBD | needs implementation |
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| Betweenness Centrality | TBD | needs implementation |
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| Triangle Count | TBD | needs implementation |
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| Subgraph Isomorphism | TBD | needs implementation |
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| Kruskell Minimum Spanning Tree | TBD | needs implementation |
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| Prim Minimum Spanning Tre | TBD | needs implementation |
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| Louvain (Community Detection) | TBD | needs implementation |
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| Label propagation (Comm. Detection) | TBD | needs implementation |
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### Graph Views
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| View | Done? | Description |
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| :-------------------------------| :---- | :-------------------------------------------------------------------------------|
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| vertexlist | Yes | Iterates over vertices |
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| incidence | Yes | Iterates over outgoing edges of a vertex |
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| neighbors | Yes | Iterates over outgoing neighbor vertices of a vertex |
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| edgelist | Yes | Iterates over edges of a graph |
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| depth_first_search | Yes | Iterates over vertices or edges of a seed vertex in depth-first order |
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| breadth_first_search | Yes | Iterates over vertices or edges of a seed vertex in breadth-first order |
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| topological_sort | No | Iterates over vertices or edges of a seed vertex in topological sort order |
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### Graph Containers
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| Container | P1709 | Description |
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| :-------------------------------| :---- | :-------------------------------------------------------------------------------|
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| compressed_graph | Yes | Compresed Sparse Row graph. High performance, static structure. |
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| dynamic_graph | No | Easy to use different containers for vertices and edges. |
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### Graph Algorithms ([P3128](https://wg21.link/P3128))
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The following algorithms are planned for the Graph Library.
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| Algorithm | Status |
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| :---------------------------------- | :-------------------------------------------------------------------------------|
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| Breadth First Search | revision scheduled |
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| Depth First Search | revision scheduled |
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| Topological Sort | implementation scheduled |
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| Dijkstra Shortest Paths | Completed |
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| Bellman-Ford Shortest Paths | Completed |
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| Triangle Counting | needs implementation |
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| Label propagation (Comm. Detection) | needs implementation |
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| Articulation Points | needs implementation |
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| Bi-Connected Components | needs implementation |
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| Connected Components | needs implementation |
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| Strongly Connected Components | needs implementation |
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| Maximal Independent Set | needs implementation |
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| Jaccard Coefficient | needs implementation |
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| Kruskell Minimum Spanning Tree | needs implementation |
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| Prim Minimum Spanning Tre | needs implementation |
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### Graph Views ([P3129](https://wg21.link/P3129) )
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| View | Description |
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| :-------------------------------| :-------------------------------------------------------------------------------|
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| vertexlist | Iterates over vertices |
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| incidence | Iterates over outgoing edges of a vertex |
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| neighbors | Iterates over outgoing neighbor vertices of a vertex |
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| edgelist | Iterates over edges of a graph |
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| depth_first_search | Iterates over vertices or edges of a seed vertex in depth-first order |
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| breadth_first_search | Iterates over vertices or edges of a seed vertex in breadth-first order |
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| topological_sort | Iterates over vertices or edges of a seed vertex in topological sort order |
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### Graph Containers ([P3131](https://wg21.link/P3130))
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| Container | Description |
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| :-------------------------------| :-------------------------------------------------------------------------------|
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| compressed_graph | Compresed Sparse Row graph. High performance, static structure. |
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| dynamic_graph | Easy to use different containers for vertices and edges. |
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| (std containers) | Use standard containers like `vector` and `list` to define a simple graph. |
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## Papers
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The following papers make up the current proposal for the Graph Library.
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| Paper | Description |
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| :---------------------------------------------------------| :-------------------------------------------------------------------------------------------------------|
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| [P3126 Overview](https://wg21.link/P3126) | Describes the big picture of what we are proposing. |
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| [P3127 Background](https://wg21.link/P3127) | Background and Terminology, provides the motivation and theoretical background underlying the proposal. |
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| [P3128 Algoritms](https://wg21.link/P3128) | Covers the initial algorithms as well as the ones we'd like to see in the future. |
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| [P3129 Views](https://wg21.link/P3129) | Helpful views for traversing a graph. |
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| [P3130 Graph Container Interface](https://wg21.link/P3130)| The core interface for uniformly accessing graph data structure and adapting to external graphs. |
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| [P3131 Graph Containers](https://wg21.link/P3130) | Includes the `compressed_graph` and how to use standard containers to define simple graphs. |
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| [P3337 Graph Comparison](https://wg21.link/P3337) | *[future]* Syntax and performance comparison to the Boost Graph Library. |
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## Acknowledgments

‎include/graph/algorithm/bellman_ford_shortest_paths.hpp

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sized_range<Predecessors> && //
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basic_edge_weight_function<G, WF, range_value_t<Distances>, Compare, Combine>
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[[nodiscard]] constexpr optional<vertex_id_t<G>> bellman_ford_shortest_paths(
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G&& g,
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const vertex_id_t<G> source,
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Distances& distances,
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Predecessors& predecessor,
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G&& g,
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vertex_id_t<G> source,
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Distances& distances,
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Predecessors& predecessor,
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WF&& weight = [](edge_reference_t<G> uv) { return range_value_t<Distances>(1); }, // default weight(uv) -> 1
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Visitor&& visitor = empty_visitor(),
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Compare&& compare = less<range_value_t<Distances>>(),
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sized_range<Distances> && //
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basic_edge_weight_function<G, WF, range_value_t<Distances>, Compare, Combine>
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[[nodiscard]] constexpr optional<vertex_id_t<G>> bellman_ford_shortest_distances(
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G&& g,
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const vertex_id_t<G> source,
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Distances& distances,
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G&& g,
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vertex_id_t<G> source,
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Distances& distances,
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WF&& weight = [](edge_reference_t<G> uv) { return range_value_t<Distances>(1); }, // default weight(uv) -> 1
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Visitor&& visitor = empty_visitor(),
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Compare&& compare = less<range_value_t<Distances>>(),

‎include/graph/algorithm/common_shortest_paths.hpp

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#include <algorithm>
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#include <numeric>
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#include <graph/detail/graph_using.hpp>
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#ifndef GRAPH_COMMON_SHORTEST_PATHS_HPP
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# define GRAPH_COMMON_SHORTEST_PATHS_HPP
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// Vertex visitor concepts
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template <class G, class Visitor>
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concept has_on_initialize_vertex = //
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concept has_on_initialize_vertex = // For exposition only
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requires(Visitor& v, vertex_descriptor<vertex_id_t<G>, vertex_reference_t<G>, void> vdesc) {
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{ v.on_initialize_vertex(vdesc) };
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};
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template <class G, class Visitor>
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concept has_on_discover_vertex = //
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concept has_on_discover_vertex = // For exposition only
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requires(Visitor& v, vertex_descriptor<vertex_id_t<G>, vertex_reference_t<G>, void> vdesc) {
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{ v.on_discover_vertex(vdesc) };
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};
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template <class G, class Visitor>
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concept has_on_examine_vertex = //
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concept has_on_examine_vertex = // For exposition only
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requires(Visitor& v, vertex_descriptor<vertex_id_t<G>, vertex_reference_t<G>, void> vdesc) {
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{ v.on_examine_vertex(vdesc) };
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};
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template <class G, class Visitor>
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concept has_on_finish_vertex = //
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concept has_on_finish_vertex = // For exposition only
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requires(Visitor& v, vertex_descriptor<vertex_id_t<G>, vertex_reference_t<G>, void> vdesc) {
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{ v.on_finish_vertex(vdesc) };
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};
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// Edge visitor concepts
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template <class G, class Visitor>
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concept has_on_examine_edge = //
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concept has_on_examine_edge = // For exposition only
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requires(Visitor& v, edge_descriptor<vertex_id_t<G>, true, edge_reference_t<G>, void> edesc) {
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{ v.on_examine_edge(edesc) };
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};
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template <class G, class Visitor>
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concept has_on_edge_relaxed = //
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concept has_on_edge_relaxed = // For exposition only
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requires(Visitor& v, edge_descriptor<vertex_id_t<G>, true, edge_reference_t<G>, void> edesc) {
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{ v.on_edge_relaxed(edesc) };
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};
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template <class G, class Visitor>
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concept has_on_edge_not_relaxed = //
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concept has_on_edge_not_relaxed = // For exposition only
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requires(Visitor& v, edge_descriptor<vertex_id_t<G>, true, edge_reference_t<G>, void> edesc) {
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{ v.on_edge_not_relaxed(edesc) };
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};
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template <class G, class Visitor>
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concept has_on_edge_minimized = //
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concept has_on_edge_minimized = // For exposition only
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requires(Visitor& v, edge_descriptor<vertex_id_t<G>, true, edge_reference_t<G>, void> edesc) {
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{ v.on_edge_minimized(edesc) };
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};
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template <class G, class Visitor>
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concept has_on_edge_not_minimized =
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concept has_on_edge_not_minimized = // For exposition only
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requires(Visitor& v, edge_descriptor<vertex_id_t<G>, true, edge_reference_t<G>, void> edesc) {
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{ v.on_edge_not_minimized(edesc) };
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};

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