[INIT]

CMakeLists.txt

+cmake_minimum_required(VERSION 3.16)
+project(igraph_community_optimal C)
+
+find_package(igraph REQUIRED)
+
+add_executable(igraph_community_optimal igraph_community_optimal.c)
+target_link_libraries(igraph_community_optimal PUBLIC igraph::igraph)

igraph_community_optimal.c

+/* -*- mode: C -*-  */
+/*
+   IGraph library.
+   Copyright (C) 2010-2012  Gabor Csardi <csardi.gabor@gmail.com>
+   334 Harvard street, Cambridge, MA 02139 USA
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc.,  51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301 USA
+
+*/
+
+#include <igraph.h>
+
+void prepare_weights_vector(igraph_vector_t* weights, const igraph_t* graph) {
+    int i, n = igraph_ecount(graph);
+    igraph_vector_resize(weights, n);
+    for (i = 0; i < n; i++) {
+        VECTOR(*weights)[i] = i % 5;
+    }
+}
+
+int main() {
+    igraph_t graph;
+
+    igraph_vector_t v;
+    igraph_real_t edges[] = { 0, 1, 0, 2, 0, 3, 0, 4, 0, 5, 0, 6, 0, 7, 0, 8,
+                              0, 10, 0, 11, 0, 12, 0, 13, 0, 17, 0, 19, 0, 21, 0, 31,
+                              1, 2, 1, 3, 1, 7, 1, 13, 1, 17, 1, 19, 1, 21, 1, 30,
+                              2, 3, 2, 7, 2, 27, 2, 28, 2, 32, 2, 9, 2, 8, 2, 13,
+                              3, 7, 3, 12, 3, 13, 4, 6, 4, 10, 5, 6, 5, 10, 5, 16,
+                              6, 16, 8, 30, 8, 32, 8, 33, 9, 33, 13, 33, 14, 32, 14, 33,
+                              15, 32, 15, 33, 18, 32, 18, 33, 19, 33, 20, 32, 20, 33,
+                              22, 32, 22, 33, 23, 25, 23, 27, 23, 32, 23, 33, 23, 29,
+                              24, 25, 24, 27, 24, 31, 25, 31, 26, 29, 26, 33, 27, 33,
+                              28, 31, 28, 33, 29, 32, 29, 33, 30, 32, 30, 33, 31, 32, 31, 33,
+                              32, 33
+                            };
+
+    igraph_vector_t membership;
+    igraph_vector_t weights;
+    igraph_real_t modularity;
+    igraph_bool_t simple;
+    int retval;
+
+    igraph_vector_view(&v, edges, sizeof(edges) / sizeof(double));
+    igraph_create(&graph, &v, 0, IGRAPH_UNDIRECTED);
+
+    igraph_vector_init(&weights, 0);
+
+    igraph_is_simple(&graph, &simple);
+    if (!simple) {
+        return 1;
+    }
+
+    igraph_vector_init(&membership, 0);
+
+    igraph_set_error_handler(&igraph_error_handler_printignore);
+
+    /* Zachary karate club, unweighted */
+    retval = igraph_community_optimal_modularity(&graph, &modularity,
+             &membership, 0);
+    if (retval == IGRAPH_UNIMPLEMENTED) {
+        return 77;
+    }
+    if (fabs(modularity - 0.4197896) > 0.0000001) {
+        return 2;
+    }
+    /* Zachary karate club, weighted */
+    prepare_weights_vector(&weights, &graph);
+    igraph_community_optimal_modularity(&graph, &modularity,
+                                        &membership, &weights);
+    if (fabs(modularity - 0.5115767) > 0.0000001) {
+        return 4;
+    }
+    igraph_destroy(&graph);
+
+    /* simple graph with loop edges, unweighted */
+    igraph_small(&graph, 6, IGRAPH_UNDIRECTED,
+                 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 0, 0, 0, 2, 2, -1);
+    igraph_community_optimal_modularity(&graph, &modularity,
+                                        &membership, 0);
+    if (fabs(modularity - 0.28125) > 0.00001) {
+        return 3;
+    }
+    /* simple graph with loop edges, weighted */
+    prepare_weights_vector(&weights, &graph);
+    igraph_community_optimal_modularity(&graph, &modularity,
+                                        &membership, &weights);
+    if (fabs(modularity - 0.36686) > 0.00001) {
+        return 5;
+    }
+    igraph_destroy(&graph);
+
+    igraph_vector_destroy(&membership);
+    igraph_vector_destroy(&weights);
+
+    return 0;
+}
+