Euclidean generator and tsp enhancements

example/Jamfile.v2

@@ -81,6 +81,7 @@ run filtered_graph_edge_range.cpp ;
 run filtered_vec_as_graph.cpp ;
 run filtered-copy-example.cpp ;
 exe fr_layout : fr_layout.cpp /boost/timer//boost_timer : [ requires cxx11_noexcept cxx11_rvalue_references sfinae_expr cxx11_auto_declarations cxx11_lambdas cxx11_unified_initialization_syntax cxx11_hdr_tuple cxx11_hdr_initializer_list cxx11_hdr_chrono cxx11_thread_local cxx11_constexpr cxx11_nullptr cxx11_numeric_limits cxx11_decltype cxx11_hdr_array cxx11_hdr_atomic cxx11_hdr_type_traits cxx11_allocator cxx11_explicit_conversion_operators ] ;
+exe geometric_graph_generator_example : geometric_graph_generator_example.cpp ;
 run gerdemann.cpp ;
 run graph.cpp ;
 run graph_as_tree.cpp ;

example/geometric_graph_generator_example.cpp

@@ -0,0 +1,59 @@
+//=======================================================================
+// Copyright 2026 Matyas W Egyhazy
+// Copyright (C) 2026 Arnaud Becheler
+// Author: Matyas W Egyhazy
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//=======================================================================
+
+#include <boost/graph/adjacency_matrix.hpp>
+#include <boost/graph/geometric_graph_generator.hpp>
+#include <boost/graph/kruskal_min_spanning_tree.hpp>
+#include <boost/graph/properties.hpp>
+#include <boost/graph/simple_point.hpp>
+
+#include <cstddef>
+#include <iostream>
+#include <random>
+#include <vector>
+
+namespace
+{
+
+using Graph = ::boost::adjacency_matrix< ::boost::undirectedS, ::boost::no_property, ::boost::property< ::boost::edge_weight_t, double > >;
+using Point = ::boost::simple_point< double >;
+using Edge = ::boost::graph_traits< Graph >::edge_descriptor;
+
+
+} // end anonymous namespace
+
+int main()
+{
+    constexpr std::size_t num_points = 20;
+
+    Graph g(num_points);
+    std::mt19937 gen(42);
+    std::uniform_real_distribution< double > coordinates(0.0, 500.0);
+    auto weight_map = ::boost::get(::boost::edge_weight, g);
+
+    ::boost::graph::make_random_geometric_graph< Point >(g, num_points,
+        coordinates, coordinates, weight_map,
+        ::boost::get(::boost::vertex_index, g), gen,
+        ::boost::graph::default_euclidean_distance{});
+
+    std::cout << "Complete geometric graph: " << ::boost::num_vertices(g) << " vertices, " << ::boost::num_edges(g) << " edges\n";
+
+    std::vector< Edge > mst;
+    ::boost::kruskal_minimum_spanning_tree(g, std::back_inserter(mst));
+
+    double total = 0.0;
+
+    for (const Edge& e : mst)
+        total += ::boost::get(weight_map, e);
+
+    std::cout << "Minimum spanning tree: " << mst.size() << " edges, total weight " << total << "\n";
+
+    return 0;
+}

include/boost/graph/geometric_graph_generator.hpp

@@ -0,0 +1,178 @@
+//=======================================================================
+// Copyright 2026 Matyas W Egyhazy
+// Copyright (C) 2026 Arnaud Becheler
+// Author: Matyas W Egyhazy
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+//=======================================================================
+
+#ifndef BOOST_GRAPH_GEOMETRIC_GRAPH_GENERATOR_HPP
+#define BOOST_GRAPH_GEOMETRIC_GRAPH_GENERATOR_HPP
+
+#include <boost/assert.hpp>
+#include <boost/concept/assert.hpp>
+#include <boost/concept_check.hpp>
+#include <boost/container_hash/hash.hpp>
+#include <boost/graph/graph_concepts.hpp>
+#include <boost/graph/graph_traits.hpp>
+#include <boost/graph/properties.hpp>
+#include <boost/graph/simple_point.hpp>
+#include <boost/static_assert.hpp>
+#include <boost/unordered/unordered_flat_set.hpp>
+
+#include <algorithm>
+#include <cstddef>
+#include <iterator>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+namespace boost
+{
+namespace graph
+{
+
+    /**
+     * Calculates the 2D Euclidean distance between two points using
+     * std::hypot.
+     *
+     * Works with any point type possessing public '.x' and '.y' members or
+     * accessors.
+     */
+    template < typename Point1, typename Point2 >
+    inline auto euclidean_distance(const Point1& p1, const Point2& p2)
+        -> decltype(std::hypot(p1.x - p2.x, p1.y - p2.y))
+    {
+        using RawType = decltype(p1.x - p2.x);
+        using CalcType = std::conditional_t< std::is_integral< RawType >::value,
+            double, RawType >;
+
+        return std::hypot(
+            static_cast< CalcType >(p1.x) - static_cast< CalcType >(p2.x),
+            static_cast< CalcType >(p1.y) - static_cast< CalcType >(p2.y));
+    }
+
+    // Functor wrapper for boost::graph::euclidean_distance to serve as a clean
+    // default
+    struct default_euclidean_distance
+    {
+        template < typename Point1, typename Point2 >
+        auto operator()(const Point1& p1, const Point2& p2) const
+            -> decltype(::boost::graph::euclidean_distance(p1, p2))
+        {
+            return ::boost::graph::euclidean_distance(p1, p2);
+        }
+    };
+
+// Connects every pair of vertices with an edge weighted by the distance between
+// the corresponding points. A common preprocessing step for TSP algorithms.
+//
+// The distance functor must be supplied by the caller. Writing an ADL wrapper
+// inside namespace boost is not possible because unqualified lookup there also
+// finds boost::distance from Boost.Range.
+//
+// Preconditions: num_vertices(g) == points.size() and g has no edges.
+// Complexity: O(V^2).
+template < typename VertexListGraph, typename PointContainer, typename WeightMap, typename VertexIndexMap, typename BinaryFunction >
+void connect_all_geometric(VertexListGraph& g, const PointContainer& points, WeightMap wmap, VertexIndexMap vmap, BinaryFunction distance)
+{
+    using Traits = ::boost::graph_traits< VertexListGraph >;
+
+    BOOST_CONCEPT_ASSERT((::boost::VertexListGraphConcept< VertexListGraph >));
+    BOOST_CONCEPT_ASSERT((::boost::MutableGraphConcept< VertexListGraph >));
+    BOOST_CONCEPT_ASSERT((::boost::RandomAccessContainerConcept< PointContainer >));
+    BOOST_CONCEPT_ASSERT((::boost::ReadablePropertyMapConcept< VertexIndexMap, typename Traits::vertex_descriptor >));
+    BOOST_CONCEPT_ASSERT((::boost::WritablePropertyMapConcept< WeightMap, typename Traits::edge_descriptor >));
+
+    BOOST_STATIC_ASSERT_MSG((!std::is_convertible< typename Traits::directed_category, ::boost::directed_tag >::value), "connect_all_geometric requires an undirected graph type.");
+
+    using WeightType = typename ::boost::property_traits< WeightMap >::value_type;
+    using IndexType = typename ::boost::property_traits< VertexIndexMap >::value_type;
+
+    BOOST_STATIC_ASSERT_MSG(!std::is_integral< WeightType >::value, "connect_all_geometric requires a non-integral weight type. Integer weights truncate distances.");
+
+    BOOST_ASSERT_MSG(num_vertices(g) == points.size(), "connect_all_geometric requires num_vertices(g) == points.size()");
+
+    using VertexIterator = typename Traits::vertex_iterator;
+    std::pair< VertexIterator, VertexIterator > verts(vertices(g));
+
+    for (VertexIterator src(verts.first); src != verts.second; ++src)
+    {
+        const IndexType src_index = get(vmap, *src);
+        VertexIterator dest(src);
+        ++dest;
+
+        for (; dest != verts.second; ++dest)
+        {
+            const IndexType dest_index = get(vmap, *dest);
+            const WeightType weight = static_cast< WeightType >(distance(points[src_index], points[dest_index]));
+            put(wmap, add_edge(*src, *dest, g).first, weight);
+        }
+    }
+}
+
+// Writes num_points distinct points to out, in generation order.
+//
+// Uniqueness is decided on the drawn coordinate pair rather than on PointType, so
+// PointType needs no hash and no equality of its own. That is equivalent as long
+// as PointType{x, y} is injective. A point type that normalises or snaps on
+// construction needs its own filter.
+//
+// Returns the number of points actually written, which is less than num_points
+// when the distributions cannot supply enough distinct values within
+// max_attempts draws. A max_attempts of zero selects a default budget.
+template < typename PointType, typename OutputIterator, typename XDistribution, typename YDistribution, typename URBG >
+std::size_t generate_unique_random_points(std::size_t num_points, XDistribution x_dist, YDistribution y_dist, OutputIterator out, URBG&& gen, std::size_t max_attempts = 0)
+{
+    using CoordType = typename XDistribution::result_type;
+
+    BOOST_STATIC_ASSERT_MSG((std::is_same< CoordType, typename YDistribution::result_type >::value), "X and Y distributions must have the same result type");
+
+    if (max_attempts == 0)
+        max_attempts = std::max< std::size_t >(10 * num_points, 100);
+
+    ::boost::unordered_flat_set< std::pair< CoordType, CoordType > > seen;
+    seen.reserve(num_points);
+
+    std::size_t attempts = 0;
+
+    while (seen.size() < num_points && attempts < max_attempts)
+    {
+        const CoordType x = x_dist(gen);
+        const CoordType y = y_dist(gen);
+
+        if (seen.insert(std::make_pair(x, y)).second)
+            *out++ = PointType { x, y };
+
+        ++attempts;
+    }
+
+    return seen.size();
+}
+
+// Populates g with num_points random points and complete geometric weights.
+//
+// Throws std::runtime_error when the distributions cannot supply num_points
+// distinct points, because a shorter point set would leave connect_all_geometric
+// indexing past the end.
+template < typename PointType, typename VertexListGraph, typename WeightMap, typename VertexIndexMap, typename XDistribution, typename YDistribution, typename URBG, typename BinaryFunction >
+void make_random_geometric_graph(VertexListGraph& g, std::size_t num_points, XDistribution x_dist, YDistribution y_dist, WeightMap weight_map, VertexIndexMap vertex_index_map, URBG&& gen, BinaryFunction distance)
+{
+    std::vector< PointType > points;
+    points.reserve(num_points);
+
+    const std::size_t generated = generate_unique_random_points< PointType >(num_points, x_dist, y_dist, std::back_inserter(points), gen);
+
+    if (generated != num_points)
+        throw std::runtime_error("make_random_geometric_graph: the given distributions cannot supply num_points distinct points");
+
+    connect_all_geometric(g, points, weight_map, vertex_index_map, distance);
+}
+
+} // end namespace graph
+} // end namespace boost
+
+#endif // BOOST_GRAPH_GEOMETRIC_GRAPH_GENERATOR_HPP

test/Jamfile.v2

@@ -71,6 +71,7 @@ alias graph_test_regular :
     [ compile filtered_graph_cc.cpp ]
     [ run filter_graph_vp_test.cpp ]
     [ run generator_test.cpp ]
+    [ run geometric_graph_generator_test.cpp ]
     [ run graph.cpp : : : <define>TEST=1 : graph_1 ]
     [ run graph.cpp : : : <define>TEST=2 : graph_2 ]
     [ run graph.cpp : : : <define>TEST=3 : graph_3 ]