Add graph references

2026-06-28 13:49:01 +01:00
parent 0a9807e448
commit a11edf0c53
2578 changed files with 868045 additions and 0 deletions
@@ -0,0 +1,179 @@
+/*
+   igraph library.
+   Copyright (C) 2025  The igraph development team <igraph@igraph.org>
+
+   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, see <https://www.gnu.org/licenses/>.
+*/
+
+#include <igraph.h>
+
+#include "test_utilities.h"
+
+void test_mycielskian(void) {
+    igraph_t g, res;
+    igraph_t groetzsch;
+    igraph_bool_t isomorphic;
+
+    igraph_famous(&groetzsch, "Groetzsch");
+
+    // k == 0 testing
+    printf("small graph, k=0\n");
+    igraph_small(
+        &g, 5, /* directed = */ false,
+        /* edge 0 */ 0, 1,
+        /* edge 1 */ 0, 3,
+        /* edge 2 */ 1, 2,
+        /* edge 3 */ 2, 4,
+        /* edge 4 */ 2, 3,
+        /* edge 5 */ 3, 4,
+        -1
+    );
+    igraph_mycielskian(&g, &res, 0);
+    print_graph(&res);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // vcount == 0, k==0 testing
+    printf("null graph, k=0\n");
+    igraph_empty(&g, 0, IGRAPH_UNDIRECTED);
+    igraph_mycielskian(&g, &res, 0);
+    print_graph(&res);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // vcount == 0, k==1 testing
+    printf("null graph, k=1\n");
+    igraph_empty(&g, 0, IGRAPH_UNDIRECTED);
+    igraph_mycielskian(&g, &res, 1);
+    print_graph(&res);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // vcount == 0, k==3 testing
+    printf("null graph, k=3\n");
+    igraph_empty(&g, 0, IGRAPH_UNDIRECTED);
+    igraph_mycielskian(&g, &res, 3);
+    print_graph(&res);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // vcount == 1, k==0 testing
+    printf("singleton graph, k=0\n");
+    igraph_empty(&g, 1, IGRAPH_UNDIRECTED);
+    igraph_mycielskian(&g, &res, 0);
+    print_graph(&res);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // checking for directed graphs for directed attribute
+    printf("small directed graph, k=0\n");
+    igraph_small(
+        &g, 5, /* directed = */ true,
+        /* edge 0 */ 0, 1,
+        /* edge 1 */ 0, 3,
+        /* edge 2 */ 1, 2,
+        /* edge 3 */ 2, 4,
+        /* edge 4 */ 2, 3,
+        /* edge 5 */ 3, 4,
+        -1
+    );
+    igraph_mycielskian(&g, &res, 0);
+    print_graph(&res);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // vcount == 1, k==3 testing --> should output a Grötzsch graph
+    printf("singleton graph, k=3\n");
+    igraph_empty(&g, 1, IGRAPH_UNDIRECTED);
+    igraph_mycielskian(&g, &res, 3);
+    print_graph(&res);
+    igraph_isomorphic(&groetzsch, &res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+    printf("\n\n");
+
+    // P_2 graph with k=2 gives the Grötzsch graph
+    printf("P_2, k=2\n");
+    igraph_ring(&g, 2, IGRAPH_UNDIRECTED, false, false);
+    igraph_mycielskian(&g, &res, 2);
+    print_graph(&res);
+    igraph_isomorphic(&groetzsch, &res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&g);
+
+    igraph_destroy(&groetzsch);
+
+    VERIFY_FINALLY_STACK();
+}
+
+void test_mycielski_graph(void) {
+    igraph_t res;
+    igraph_t expected_res;
+    igraph_bool_t isomorphic;
+
+    // k == 0 testing --> should be a null graph
+    igraph_mycielski_graph(&res, 0);
+    igraph_empty(&expected_res, 0, IGRAPH_UNDIRECTED);
+    igraph_isomorphic(&res, &expected_res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&expected_res);
+
+    //should be a vertex
+    igraph_mycielski_graph(&res, 1);
+    igraph_empty(&expected_res, 1, IGRAPH_UNDIRECTED);
+    igraph_isomorphic(&res, &expected_res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&expected_res);
+
+    // should be a path
+    igraph_mycielski_graph(&res, 2);
+    igraph_ring(&expected_res, 2, IGRAPH_UNDIRECTED, false, false);
+    igraph_isomorphic(&res, &expected_res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&expected_res);
+
+    // should be a 5-cycle
+    igraph_mycielski_graph(&res, 3);
+    igraph_ring(&expected_res, 5, IGRAPH_UNDIRECTED, false, true);
+    igraph_isomorphic(&res, &expected_res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&expected_res);
+
+    // should be the Groetzsch graph
+    igraph_mycielski_graph(&res, 4);
+    igraph_famous(&expected_res, "Groetzsch");
+    igraph_isomorphic(&res, &expected_res, &isomorphic);
+    IGRAPH_ASSERT(isomorphic);
+    igraph_destroy(&res);
+    igraph_destroy(&expected_res);
+
+    VERIFY_FINALLY_STACK();
+}
+
+int main(void) {
+    test_mycielskian();
+    test_mycielski_graph();
+}