#include <igraph.h>

int main(void) {

igraph_t graph;

igraph_vector_int_t dimvector;

igraph_vector_int_t edges;

igraph_vector_bool_t periodic;

igraph_real_t avg_path_len;

igraph_vector_int_init(&dimvector, 2);

VECTOR(dimvector)[0]=30;

VECTOR(dimvector)[1]=30;

igraph_vector_bool_init(&periodic, 2);

igraph_vector_bool_fill(&periodic, true);

igraph_square_lattice(&graph, &dimvector, 0, IGRAPH_UNDIRECTED, /* mutual= */ false, &periodic);

igraph_average_path_length(&graph, &avg_path_len, NULL, IGRAPH_UNDIRECTED, /* unconn= */ true);

printf("Average path length (lattice): %g\n", (double) avg_path_len);

igraph_rng_seed(igraph_rng_default(), 42); /* seed RNG before first use */

igraph_vector_int_init(&edges, 20);

for (igraph_integer_t i=0; i < igraph_vector_int_size(&edges); i++) {

VECTOR(edges)[i] = RNG_INTEGER(0, igraph_vcount(&graph) - 1);

}

igraph_add_edges(&graph, &edges, NULL);

igraph_average_path_length(&graph, &avg_path_len, NULL, IGRAPH_UNDIRECTED, /* unconn= */ true);

printf("Average path length (randomized lattice): %g\n", (double) avg_path_len);

igraph_vector_bool_destroy(&periodic);

igraph_vector_int_destroy(&dimvector);

igraph_vector_int_destroy(&edges);

igraph_destroy(&graph);

return 0;

}