igraph 0.10.0

This release focuses on infrastructural improvements, stability, and making the igraph interface more consistent, more predictable and easier to use. It contains many API-breaking changes and function renamings, in preparation for a future 1.0 release, at which point the API will become stable. Changes in this direction are likely to continue through a 0.11 release. It is recommended that you migrate your code from 0.9 to 0.10 soon, to make the eventual transition to 1.0 easier.

Some of the highlights are:

• A consistent use of igraph_integer_t for all indices and most integer quantities, both in the API and internally. This type is 64-bit by default on all 64-bit systems, bringing support for very large graphs with more than 2 billion vertices. Previously, vertex and edge indices were often represented as igraph_real_t. The move to an igraph_integer_t also implies a change from igraph_vector_t to igraph_vector_int_t in many functions.
• The random number generation framework has been overhauled. Sampling from the full range of igraph_integer_t is now possible. Similarly, the sampling of random reals has been improved to utilize almost the full range of the mantissa of an igraph_real_t.
• There is a new fully memory-managed container type for lists of vectors (igraph_vector_list_t), replacing most previous uses of the non-managed igraph_vector_ptr_t. Functions that previously used igraph_vector_ptr_t to return results and relied on the user to manage memory appropriately are now using igraph_vector_list_t, igraph_graph_list_t or similar and manage memory on their own.
• Some simple graph properties, such as whether a graph contains self-loops or multi-edges, or whether it is connected, are now cached in the graph data structure. Querying these properties for a second time will take constant computational time. The igraph_invalidate_cache() function is provided for debugging purposes. It will invaidate all cache entries.
• File format readers are much more robust and more tolerant of invalid input.
• igraph is much more resilient to overflow errors.
• Many improvements to robustness and reliability, made possible by internal refactorings.

Breaking changes

• igraph now requires CMake 3.18 or later.
• In order to facilitate the usage of graphs with more than 2 billion vertices and edges, we have made the size of the igraph_integer_t data type to be 32 bits on 32-bit platforms and 64 bits on 64-bit platforms by default. You also have the option to compile a 32-bit igraph variant on a 64-bit platform by changing the IGRAPH_INTEGER_SIZE build variable in CMake to 32.
• igraph_bool_t is now a C99 bool and not an int. Similarly, igraph_vector_bool_t now consumes sizeof(bool) bytes per entry only, not sizeof(int). The standard constants true and false may be used for Boolean values for readability.
• The random number generator interface, igraph_rng_type_t, has been overhauled. Check the declaration of the type for details.
• The default random number generator has been changed from Mersenne Twister to PCG32.
• Functions related to spectral coarse graining (i.e. all functions starting with igraph_scg_...) were separated into a project of its own. If you wish to keep on using these functions, please refer to the repository hosting the spectral coarse graining code at https://github.com/igraph/igraph-scg . The spectral coarse graining code was updated to support igraph 0.10.
• Since igraph_integer_t aims to be the largest integer size that is feasible on a particular platform, there is no need for generic data types based on long int any more. The long variants of generic data types (e.g., igraph_vector_long_t) are therefore removed; you should use the corresponding int variant instead, whose elements are of type igraph_integer_t.
• Generic data types based on float were removed as they were not used anywhere in the library.
• Several igraph functions that used to take a long int or return a long int now takes or returns an igraph_integer_t instead to make the APIs more consistent. Similarly, igraph functions that used igraph_vector_t for arguments that take or return integral vectors (e.g., vertex or edge indices) now take igraph_vector_int_t instead. Graph-related functions where the API was changed due to this reason are listed below, one by one.
• Similarly, igraph functions that used to accept the long variant of a generic igraph data type (e.g., igraph_vector_long_t) now take the int variant of the same data type.
• The type igraph_stack_ptr_t and its associated functions were removed. Use igraph_vector_ptr_t and associated functions instead.
• Error handlers should no longer perform a longjmp(). Doing so will introduce memory leaks, as resource cleanup is now done in multiple stages, through multiple calls to the error handler. Thus, the error handler should either abort execution immediately (as the default handler does), or report the error, call IGRAPH_FINALLY_FREE(), and return normally.
• Most callback functions now return an error code. In previous versions they returned a boolean value indicating whether to terminate the search. A request to stop the search is now indicated with the special return code IGRAPH_STOP.
• igraph_add_edges() now uses an igraph_vector_int_t for its edges parameter.
• igraph_adjacency() no longer accepts a negative number of edges in its adjacency matrix. When negative entries are found, an error is generated.
• igraph_adjacency() gained an additional loops argument that lets you specify whether the diagonal entries should be ignored or should be interpreted as raw edge counts or twice the number of edges (which is common in linear algebra contexts).
• igraph_all_minimal_st_separators() now returns the separators in an igraph_vector_int_list_t containing igraph_vector_int_t vectors.
• igraph_all_st_cuts() and igraph_all_st_mincuts() now return the cuts in an igraph_vector_int_list_t containing igraph_vector_int_t vectors.
• igraph_arpack_unpack_complex() now uses igraph_integer_t for its nev argument instead of long int.
• igraph_articulation_points() now uses an igraph_vector_int_t to return the list of articulation points, not an igraph_vector_t.
• igraph_assortativity_nominal() now accepts vertex types in an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_asymmetric_preferennce_game() now uses an igraph_vector_int_t to return the types of the nodes in the generated graph.
• igraph_atlas() now uses igraph_integer_t for its number argument.
• igraph_automorphism_group() now returns the generators in an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
• igraph_barabasi_game(), igraph_barabasi_aging_game(), igraph_recent_degree_game() and igraph_recent_degree_aging_game() now use an igraph_vector_int_t for the out-degree sequence of the nodes being generated instead of an igraph_vector_t.
• igraph_bfs() now takes an igraph_vector_int_t for its roots, restricted, order, father, pred, succ and dist arguments instead of an igraph_vector_t.
• igraph_bfs_simple() now takes igraph_vector_int_t for its vids, layers and parents arguments instead of an igraph_vector_t.
• igraph_bfs_simple() now returns -1 in parents for the root node of the traversal, and -2 for unreachable vertices. This is now consistent with other functions that return a parent vector.
• igraph_biconnected_components() now uses an igraph_vector_int_t to return the list of articulation points, not an igraph_vector_t. Also, the container used for the edges and vertices of the components is now an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
• igraph_bipartite_projection() now uses igraph_vector_int_t to return multiplicity1 and multiplicity2, not igraph_vector_t.
• igraph_bridges() now uses an igraph_vector_int_t to return the list of bridges, not an igraph_vector_t.
• igraph_callaway_traits_game() returns the node types in an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_canonical_permutation() now uses an igraph_vector_int_t for its labeling parameter.
• igraph_cattribute_list() now uses igraph_vector_int_t to return gtypes, vtypes and etypes.
• igraph_cited_type_game() now uses an igraph_vector_int_t for its types parameter.
• igraph_citing_cited_type_game() now uses an igraph_vector_int_t for its
  types parameter.
• igraph_clique_handler_t now uses an igraph_vector_int_t for its clique parameter, and must return an igraph_error_t. Use IGRAPH_STOP as the return code to terminate the search prematurely. The vector that the handler receives is owned by the clique search routine. If you want to hold on to the vector for a longer period of time, you need to make a copy of it in the handler. Cliques passed to the callback are marked as const as a reminder to this change.
• The res parameter of igraph_cliques() is now an igraph_vector_int_list_t.
• Callbacks used by igraph_cliques_callback() need to be updated to account for the fact that the callback does not own the clique passed to it any more; the callback needs to make a copy if it wants to hold on to the clique for a longer period of time. If the callback does not need to store the clique, it does not need to do anything any more, and it must not destroy or free the clique.
• igraph_closeness() and igraph_closeness_cutoff() now use an igraph_vector_int_t to return reachable_count, not an igraph_vector_t.
• igraph_cohesive_blocks() now uses an igraph_vector_int_t to return the mapping from block indices to parent block indices, and the cohesion; also, it uses an igraph_vector_int_list_t to return the blocks themselves instead of a pointer vector of igraph_vector_t.
• The igraph_community_eb_get_merges() bridges parameter now starts the indices into the edge removal vector at 0, not 1.
• The igraph_community_eb_get_merges() now reports an error when not all edges in the graph are removed, instead of a nonsensical result.
• igraph_community_edge_betweenness() now uses an igraph_vector_int_t to return the edge IDs in the order of their removal as well as the list of edge IDs whose removal broke a single component into two.
• igraph_community_fluid_communities() does not provide the modularity in a separate output argument any more; use igraph_modularity() to retrieve the modularity if you need it.
• igraph_community_infomap() now uses igraph_integer_t for its nb_trials argument.
• igraph_community_label_propagation() now uses an igraph_vector_int_t for its initial parameter. It also takes a mode argument that specifies how labels should be propagated along edges (forward, backward or ignoring edge directions).
• igraph_community_label_propagation() does not provide the modularity in a separate output argument any more; use igraph_modularity() to retrieve the modularity if you need it.
• igraph_community_leiden() has an additional parameter to indicate the number of iterations to perform (PR #2177).
• igraph_community_walktrap(), igraph_community_edge_betweenness(), igraph_community_eb_get_merges(), igraph_community_fastgreedy(), igraph_community_to_membership(), igraph_le_community_to_membership(), igraph_community_leading_eigenvector() now use an igraph_vector_int_t for their merges parameter.
• igraph_community_walktrap() now uses igraph_integer_t for its steps argument.
• igraph_coreness() now uses an igraph_vector_int_t to return the coreness
  values.
• igraph_convex_hull() now uses an igraph_vector_int_t to return the indices of the input vertices that were chosen to be in the convex hull.
• igraph_correlated_game() and igraph_correlated_pair_game() now take an igraph_vector_int_t as the permutation vector, not an igraph_vector_t.
• igraph_create() now uses an igraph_vector_int_t for its edges parameter.
• igraph_create_bipartite() now uses an igraph_vector_int_t for its edges parameter.
• igraph_compose() now returns the edge maps in an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_count_multiple() now returns the multiplicities in an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_decompose() now uses an igraph_integer_t for its maxcompno and minelements arguments instead of a long int.
• igraph_degree() now uses an igraph_vector_int_t to return the degrees. If you need the degrees in a vector containing floating-point numbers instead (e.g., because you want to pass them on to some other function that takes an igraph_vector_t), use igraph_strength() instead with a null weight vector.
• igraph_degree_sequence_game() now takes degree sequences represented as igraph_vector_int_t instead of igraph_vector_t.
• igraph_degseq_t, used by igraph_degree_sequence_game(), uses new names for its constants. The old names are deprecated, but retained for compatibility. See igraph_constants.h to see which new name corresponds to which old one.
• igraph_delete_vertices_idx() now uses igraph_vector_int_t vectors to return the mapping and the inverse mapping of old vertex IDs to new ones.
• igraph_deterministic_optimal_imitation() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
• igraph_dfs() now takes an igraph_vector_int_t for its order, order_out, father and dist arguments instead of an igraph_vector_t. Furthermore, these vectors will contain -2 for vertices that have not been visited; in earlier versions, they used to contain NaN instead. Note that -1 is still used in the father vector to indicate the root of a DFS tree.
• igraph_diameter() and igraph_diameter_dijkstra() now use igraph_vector_int_t vectors to return the list of vertex and edge IDs in the diameter.
• igraph_dominator_tree() now takes an igraph_vector_int_t for its dom and leftout arguments instead of an igraph_vector_t.
• igraph_dyad_census() now uses igraph_real_t instead of igraph_integer_t for its output arguments, and it no longer returns -1 when overflow occurs.
• igraph_edges() now takes an igraph_vector_int_t for its edges argument instead of an igraph_vector_t.
• igraph_es_multipairs() was removed; you can use the newly added igraph_es_all_between() instead.
• igraph_establishment_game() now takes an igraph_vector_int_t for its node_type_vec argument instead of an igraph_vector_t.
• igraph_eulerian_path() and igraph_eulerian_cycle() now use igraph_vector_int_t to return the list of edge and vertex IDs participating in an Eulerian path or cycle instead of an igraph_vector_t.
• igraph_feedback_arc_set() now uses an igraph_vector_int_t to return the IDs of the edges in the feedback arc set instead of an igraph_vector_t.
• igraph_get_adjacency() no longer has the eids argument, which would produce an adjacency matrix where non-zero values were 1-based (not 0-based) edge IDs. If you need a matrix with edge IDs, create it manually.
• igraph_get_adjacency_sparse() now returns the sparse adjacency matrix in an igraph_sparsemat_t structure, and it assumes that the input matrix is initialized for sake of consistency with other igraph functions.
• igraph_get_adjacency() and igraph_get_adjacency_sparse() now has a loops argument that lets the user specify how loop edges should be handled.
• igraph_get_edgelist() now uses an igraph_vector_int_t for its res parameter.
• igraph_get_eids() now uses igraph_vector_int_t to return lists of edge IDs and to receive lists of vertex IDs.
• The path argument of igraph_get_eids() was removed. You can replicate the old behaviour by constructing the list of vertex IDs explicitly from the path by duplicating each vertex in the path except the first and last ones. A helper function called igraph_expand_path_to_pairs() is provided to ease the transition.
• igraph_get_eids_multi() was removed as its design was fundamentally broken; there was no way to retrieve the IDs of all edges between a specific pair of vertices without knowing in advance how many such edges there are in the graph. Use igraph_get_all_eids_between() instead.
• igraph_get_incidence() now returns the vertex IDs corresponding to the rows and columns of the incidence matrix as igraph_vector_int_t.
• igraph_get_shortest_path(), igraph_get_shortest_path_bellman_ford() and igraph_get_shortest_path_dijkstra() now use igraph_vector_int_t vectors to return the list of vertex and edge IDs in the shortest path.
• igraph_get_shortest_paths(), igraph_get_shortest_paths_dijkstra() and igraph_get_shortest_paths_bellman_ford() now use an igraph_vector_int_t to return the predecessors and inbound edges instead of an igraph_vector_long_t.
• The functions igraph_get_all_shortest_paths(), igraph_get_all_shortest_paths_dijkstra(), igraph_get_shortest_paths(), igraph_get_shortest_paths_bellman_ford() and igraph_get_shortest_paths_dijkstra() now return paths in an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
• The vector of parents in igraph_get_shortest_paths(), igraph_get_shortest_paths_bellman_ford() and igraph_get_shortest_paths_dijkstra() now use -1 to represent the starting vertex, and -2 for unreachable vertices.
• The maps parameters in igraph_get_isomorphisms_vf2() and igraph_get_subisomorphisms_vf2() are now of type igraph_vector_int_list_t.
• igraph_get_stochastic() now has an additional weights argument for edge weights.
• igraph_get_stochastic_sparse() now returns the sparse adjacency matrix in an igraph_sparsemat_t structure, and it assumes that the input matrix is initialized for sake of consistency with other igraph functions. It also received an additional weights argument for edge weights.
• igraph_girth() now uses an igraph_vector_int_t for its circle parameter.
• igraph_girth() now uses igraph_real_t as the return value so we can return infinity for graphs with no cycles (instead of zero).
• The cliques parameters of type igraph_vector_ptr_t in igraph_graphlets(), igraph_graphlets_candidate_basis() and igraph_graphlets_project() were changed to an igraph_vector_int_list_t.
• igraph_hrg_init() and igraph_hrg_resize() now takes an igraph_integer_t as their size arguments instead of an int.
• igraph_hrg_consensus() now returns the parent vector in an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_hrg_create() now takes a vector of probabilities corresponding to the internal nodes of the dendogram. It used to also take probabilities for the leaf nodes and then ignore them.
• igraph_hrg_predict() now uses an igraph_vector_int_t for its edges parameter.
• igraph_hrg_sample() now always samples a single graph only. Use igraph_hrg_sample_many() if you need more than one sample, and call igraph_hrg_fit() beforehand if you do not have a HRG model but only a single input graph.
• igraph_hrg_size() now returns an igraph_integer_t instead of an int.
• igraph_incidence() does not accept negative incidence counts any more.
• igraph_incident() now uses an igraph_vector_int_t for its eids parameter.
• The res parameter in igraph_independent_vertex_sets() is now an igraph_vector_int_list_t.
• igraph_induced_subgraph_map() now uses igraph_vector_int_t vectors to return the mapping and the inverse mapping of old vertex IDs to new ones.
• igraph_intersection() now uses an igraph_vector_int_t for its edge_map1 and edge_map2 parameters.
• The edgemaps parameter of igraph_intersection_many() is now an igraph_vector_int_list_t instead of a pointer vector.
• igraph_is_chordal() now uses an igraph_vector_int_t for its alpha, alpham1 and fill_in parameters.
• igraph_is_graphical() and igraph_is_bigraphical() now take degree sequences represented as igraph_vector_int_t instead of igraph_vector_t.
• igraph_is_matching(), igraph_is_maximal_matching() and igraph_maximum_bipartite_matching now use an igraph_vector_int_t to return the matching instead of an igraph_vector_long_t.
• igraph_is_mutual() has an additional parameter which controls whether directed self-loops are considered mutual.
• The vids parameter for igraph_isoclass_subgraph() is now an igraph_vector_int_t instead of igraph_vector_t.
• igraph_isomorphic_vf2(), igraph_get_isomorphisms_vf2_callback() (which used to be called igraph_isomorphic_function_vf2()) and igraph_isohandler_t now all use igraph_vector_int_t for their map12 and map21 parameters.
• The cliques parameter of type igraph_vector_ptr_t in igraph_largest_cliques() was changed to an igraph_vector_int_list_t.
• The res parameters of type igraph_vector_ptr_t in igraph_largest_independent_vertex_sets() and igraph_largest_weighted_cliques() were changed to an igraph_vector_int_list_t.
• The dimension vector parameter for igraph_square_lattice() (used to be igraph_lattice()) is now an igraph_vector_int_t instead of igraph_vector_t.
• The maxiter parameter of igraph_layout_bipartite() is now an igraph_integer_t instead of long int.
• The fixed parameter of igraph_layout_drl() and igraph_layout_drl_3d() was removed as it has never been implemented properly.
• The width parameter of igraph_layout_grid() is now an igraph_integer_t instead of long int.
• The width and height parameters of igraph_layout_grid_3d() are now igraph_integer_t instead of long int.
• The dimension parameter of igraph_layout_mds() is now an igraph_integer_t instead of long int.
• The roots and rootlevel parameters of igraph_layout_reingold_tilford() are now igraph_vector_int_t instead of igraph_vector_t.
• The roots and rootlevel parameters of igraph_layout_reingold_tilford_circular() are now igraph_vector_int_t instead of igraph_vector_t.
• The order parameter of igraph_layout_star() is now an igraph_vector_int_t instead of an igraph_vector_t.
• The maxiter parameter of igraph_layout_sugiyama() is now an igraph_integer_t instead of long int. Also, the function now uses an igraph_vector_int_t for its extd_to_orig_eids parameter.
• The shifts parameter of igraph_lcf_vector() is now an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_matrix_minmax(), igraph_matrix_which_minmax(), igraph_matrix_which_min() and igraph_matrix_which_max() no longer return an error code. The return type is now void. These functions never fail.
• igraph_maxflow() now uses an igraph_vector_int_t for its cut, partition and partition2 parameters.
• The igraph_maxflow_stats_t struct now contains igraph_integer_t values instead of int ones.
• The res parameters in igraph_maximal_cliques() and igraph_maximal_cliques_subset() are now of type igraph_vector_int_list_t.
• Callbacks used by igraph_maximal_cliques_callback() need to be updated to account for the fact that the callback does not own the clique passed to it any more; the callback needs to make a copy if it wants to hold on to the clique for a longer period of time. If the callback does not need to store the clique, it does not need to do anything any more, and it must not destroy or free the clique.
• The res parameter in igraph_maximal_independent_vertex_sets() is now an igraph_vector_int_list_t.
• igraph_maximum_cardinality_search() now uses an igraph_vector_int_t for its alpha and alpham1 arguments.
• igraph_mincut() now uses an igraph_vector_int_t for its cut, partition and partition2 parameters.
• igraph_moran_process() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
• Motif callbacks of type igraph_motifs_handler_t now take an igraph_vector_int_t with the vertex IDs instead of an igraph_vector_t, and use igraph_integer_t for the isoclass parameter.
• Motif functions now use igraph_integer_t instead of int for their size parameter.
• igraph_neighborhood_size() now uses an igraph_vector_int_t for its res parameter.
• The res parameter of igraph_neighborhood() is now an igraph_vector_int_list_t.
• igraph_neighbors() now uses an igraph_vector_int_t for its neis parameter.
• igraph_permute_vertices() now takes an igraph_vector_int_t as the permutation vector.
• igraph_power_law_fit() does not calculate the p-value automatically any more because the previous estimation method did not match the results from the original paper of Clauset, Shalizi and Newman (2009) and the implementation of the method outlined in the paper runs slower than the previous naive estimate. A separate function named igraph_plfit_result_calculate_p_value() is now provided for calculating the p-value. The automatic selection of the x_min cutoff also uses a different method than earlier versions. As a consequence, results might be slightly different if you used tests where the x_min cutoff was selected automatically. The new behaviour is now consistent with the defaults of the underlying plfit library.
• igraph_preference_game() now uses an igraph_vector_int_t to return the types of the nodes in the generated graph.
• igraph_random_walk() now uses an igraph_vector_int_t for its results. Also, the function now takes both vertices and edges as parameters. It can return IDs of vertices and/or edges on the walk. The function now takes weights as a parameter to support weighted graphs.
• igraph_random_edge_walk() now uses an igraph_vector_int_t for its edgewalk parameter.
• igraph_read_graph_dimacs_flow() now uses an igraph_vector_int_t for its label parameter.
• igraph_read_graph_graphml() now uses igraph_integer_t for its index argument.
• igraph_read_graph_pajek() now creates a Boolean type attribute for bipartite graphs. Previously it created a numeric attribute.
• igraph_realize_degree_sequence() now uses an igraph_vector_int_t for its outdeg and indeg parameters.
• igraph_reindex_membership() now uses an igraph_vector_int_t for its new_to_old parameter.
• igraph_rng_seed() now requires an igraph_uint_t as its seed arguments. RNG implementations are free to use only the lower bits of the seed if they do not support 64-bit seeds.
• igraph_rngtype_rand (i.e. the RNG that is based on BSD rand()) was removed due to poor statistical properties that sometimes resulted in weird artifacts like all-even "random" numbers when igraph's usage patterns happened to line up with the shortcomings of the rand() generator in a certain way.
• igraph_roulette_wheel_imitation() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
• igraph_similarity_dice_pairs() now uses an igraph_vector_int_t for its pairs parameter.
• igraph_similarity_jaccard_pairs() now uses an igraph_vector_int_t for its pairs parameter.
• igraph_simple_interconnected_islands_game() does not generate multi-edges between islands any more.
• igraph_sort_vertex_ids_by_degree() and igraph_topological_sorting() now use an igraph_vector_int_t to return the vertex IDs instead of an igraph_vector_t.
• igraph_spanning_tree(), igraph_minimum_spanning_tree() and igraph_random_spanning_tree() now all use an igraph_vector_int_t to return the vector of edge IDs in the spanning tree instead of an igraph_vector_t.
• igraph_sparsemat_cholsol(), igraph_sparsemat_lusol(), igraph_sparsemat_symbqr() and igraph_sparsemat_symblu() now take an igraph_integer_t as their order parameter.
• igraph_sparsemat_count_nonzero() and igraph_sparsemat_count_nonzerotol() now return an igraph_integer_t.
• igraph_sparsemat_is_symmetric() now returns an error code and the result itself is provided in an output argument.
• The values argument of igraph_sparsemat_transpose() was removed; now the function always copies the values over to the transposed matrix.
• igraph_spmatrix_t and related functions were removed as they mostly duplicated functionality that was already present in igraph_sparsemat_t. Functions that used igraph_spmatrix_t in the library now use igraph_sparsemat_t.
• igraph_stochastic_imitation() now expects the list of strategies in an igraph_vector_int_t instead of an igraph_int_t.
• igraph_st_mincut() now uses an igraph_vector_int_t for its cut, partition and partition2 parameters.
• igraph_st_vertex_connectivity() now ignores edges between source and target for IGRAPH_VCONN_NEI_IGNORE
• igraph_strvector_get() now returns strings in the return value, not in an output argument.
• igraph_subcomponent() now uses an igraph_integer_t for the seed vertex instead of an igraph_real_t. It also uses an igraph_vector_int_t to return the list of vertices in the same component as the seed vertex instead of an igraph_vector_t.
• igraph_subisomorphic_vf2(), igraph_get_subisomorphisms_vf2_callback() (which used to be called igraph_subisomorphic_function_vf2()) and igraph_isomorphic_bliss() now all use igraph_vector_int_t for their map12 and map21 parameters.
• The maps parameters in igraph_subisomorphic_lad(), igraph_get_isomorphisms_vf2() and igraph_get_subisomorphisms_vf2() are now of type igraph_vector_int_list_t.
• igraph_subisomorphic_lad() now uses an igraph_vector_int_t for its map parameter. Also, its domains parameter is now an igraph_vector_int_list_t instead of a pointer vector containing igraph_vector_t objects.
• igraph_unfold_tree() now uses an igraph_vector_int_t for its vertex_index and roots parameters.
• igraph_union() now uses an igraph_vector_int_t for its edge_map1 and edge_map2 parameters.
• The edgemaps parameter of igraph_union_many() is now an igraph_vector_int_list_t instead of a pointer vector.
• igraph_vector_init_copy() was refactored to take another vector that the newly initialized vector should copy. The old array-based initialization function is now called igraph_vector_init_array().
• igraph_vector_ptr_init_copy() was renamed to igraph_vector_ptr_init_array() for sake of consistency.
• igraph_vs_vector(), igraph_vss_vector() and igraph_vs_vector_copy() now all take an igraph_vector_int_t as the vector of vertex IDs, not an igraph_vector_t. Similarly, igraph_vs_as_vector() now returns the vector of matched vertex IDs in an igraph_vector_int_t, not an igraph_vector_t.
• The res parameter of igraph_weighted_cliques() is now an igraph_vector_int_list_t.
• igraph_write_graph_dimacs_flow() now uses igraph_integer_t for the source and target vertex index instead of a long int.
• igraph_vector_*(), igraph_matrix_*(), igraph_stack_*(), igraph_array_*() and several other generic igraph data types now use igraph_integer_t for indexing, not long int. Please refer to the headers for the exact details; the list of affected functions is too large to include here.
• igraph_vector_minmax() and igraph_vector_which_minmax() no longer return an error code. The return type is now void. These functions never fail.
• igraph_vector_order() was removed; use igraph_vector_int_pair_order() instead. (The original function worked for vectors containing integers only).
• igraph_vector_resize_min() and igraph_matrix_resize_min() no longer return an error code (return type is now void). The vector or matrix is always left in a consistent state by these functions, with all data intact, even if releasing unused storage is not successful.
• igraph_vector_qsort_ind() and its variants now take an igraph_order_t enum instead of a boolean to denote whether the order should be ascending or descending.
• igraph_weighted_adjacency() now returns the weights in a separate vector instead of storing it in a vertex attribute. The reason is twofold: first, the previous solution worked only with the C attribute handler (not the ones from the higher-level interfaces), and second, it wasn't consistent with other igraph functions that use weights provided as separate arguments.
• The loops argument of igraph_weighted_adjacency() was converted to an igraph_loops_t for sake of consistency with igraph_adjacency() and igraph_get_adjacency().
• igraph_write_graph_gml() takes an additional bitfield parameter controlling some aspects of writing the GML file.
• The add_edges() function in the attribute handler now takes an igraph_vector_int_t for its edges parameter instead of an igraph_vector_t. The add_vertices() function now takes an igraph_integer_t for the vertex count instead of a long int. The combine_vertices() and combine_edges() functions now take an igraph_vector_ptr_t containing vectors of type igraph_vector_int_t in their merges parameters. The get_info() function now uses igraph_vector_int_t to return the types of the graph, vertex and edge attribute types. The permute_vertices() and permute_edges() functions in the attribute handler tables now take an igraph_vector_int_t instead of an igraph_vector_t for the index vectors. These are relevant only to maintainers of higher level interfaces to igraph; they should update their attribute handlers accordingly.
• igraph functions that interface with external libraries such as BLAS or LAPACK may now fail if the underlying BLAS or LAPACK implementation cannot handle the size of input vectors or matrices (BLAS and LAPACK are usually limited to vectors whose size fits in an int). igraph_blas_dgemv() and igraph_blas_dgemv_array() thus now return an igraph_error_t, which may be set to IGRAPH_EOVERFLOW if the input vectors or matrices are too large.
• Functions that used an igraph_vector_t to represent cluster size and cluster membership now use an igraph_vector_int_t instead. These are:
  • igraph_connected_components() (used to be igraph_clusters() in 0.9 and before)
  • igraph_community_eb_get_merges()
  • igraph_community_edge_betweenness()
  • igraph_community_fastgreedy()
  • igraph_community_fluid_communities()
  • igraph_community_infomap()
  • igraph_community_label_propagation()
  • igraph_community_leading_eigenvector()
  • igraph_community_leiden()
  • igraph_community_multilevel()
  • igraph_community_optimal_modularity()
  • igraph_community_spinglass()
  • igraph_community_spinglass_single()
  • igraph_community_to_membership()
  • igraph_community_walktrap()
  • igraph_compare_communities()
  • igraph_le_community_to_membership()
  • igraph_modularity()
  • igraph_reindex_membership()
  • igraph_split_join_distance()
  • igraph_community_multilevel() additionally uses a igraph_matrix_int_t instead of igraph_matrix_t() for its memberships parameter.
• IGRAPH_TOTAL was removed from the igraph_neimode_t enum; use the equivalent IGRAPH_ALL instead.

Added

• A new integer type, igraph_uint_t has been added. This is the unsigned pair of igraph_integer_t and they are always consistent in size.
• A new container type, igraph_vector_list_t has been added, replacing most uses of igraph_vector_ptr_t in the API where it was used to hold a variable-length list of vectors. The type contains igraph_vector_t objects, and it is fully memory managed (i.e. its contents do not need to be allocated and destroyed manually). There is also a variant named igraph_vector_int_list_t for vectors of igraph_vector_int_t objects.
• A new container type, igraph_matrix_list_t has been added, replacing most uses of igraph_vector_ptr_t in the API where it was used to hold a variable-length list of matrices. The type contains igraph_matrix_t objects, and it is fully memory managed (i.e. its contents do not need to be allocated and destroyed manually).
• A new container type, igraph_graph_list_t has been added, replacing most uses of igraph_vector_ptr_t in the API where it was used to hold a variable-length list of graphs. The type contains igraph_t objects, and it is fully memory managed (i.e. its contents do not need to be allocated and destroyed manually).
• The vector container type, igraph_vector_t, has been extended with a new variant whose functions all start with igraph_vector_fortran_int_.... This vector container can be used for interfacing with Fortran code as it guarantees that the integers in the vector are compatible with Fortran integers. Note that igraph_vector_int_t is not suitable any more, as the elements of igraph_vector_int_t are of type igraph_integer_t, whose size may differ on 32-bit and 64-bit platforms, depending on how igraph was compiled.
• igraph_adjlist_init_from_inclist() to create an adjacency list from an already existing incidence list by resolving edge IDs to their corresponding endpoints. This function is useful for algorithms when both an adjacency and an incidence list is needed and they should be in the same order.
• igraph_almost_equals() and igraph_cmp_epsilon() to compare floating point numbers with a relative tolerance.
• igraph_betweenness_subset() and igraph_edge_betweenness_subset() calculates betweenness and edge betweenness scores using shortest paths between a subset of vertices only (#1711, thanks to @guyroznb)
• igraph_blas_dgemm() to multiply two matrices.
• igraph_calloc() and igraph_realloc() are now publicly exposed; these functions provide variants of calloc() and realloc() that can safely be deallocated within igraph functions.
• igraph_circulant() to create circulant graphs (#1856, thanks to @Gomango999).
• igraph_complex_almost_equals() to compare complex numbers with a relative tolerance.
• igraph_eccentricity_dijkstra() finds the longest weighted path length among all shortest paths between a set of vertices.
• igraph_enter_safelocale() and igraph_exit_safelocale() for temporarily setting the locale to C. Foreign format readers and writers require a locale which uses a decimal point instead of decimal comma.
• igraph_es_all_between() to create an edge selector that selects all edges between a pair of vertices.
• igraph_full_multipartite() generates full multipartite graphs (a generalization of bipartite graphs to multiple groups).
• igraph_fundamental_cycles() computes a fundamental cycle basis (experimental).
• igraph_generalized_petersen() to create generalized Petersen graphs (#1844, thanks to @alexsyou).
• igraph_get_all_eids_between() returns the IDs of all edges between a pair of vertices.
• igraph_get_k_shortest_paths() finds the k shortest paths between a source and a target vertex.
• igraph_get_laplacian() and igraph_get_laplacian_sparse() return the Laplacian matrix of the graph as a dense or sparse matrix, with various kinds of normalizations. They replace the now-deprecated igraph_laplacian() function. This makes the API consistent with igraph_get_adjacency() and igraph_get_adjacency_sparse().
• igraph_get_widest_path(), igraph_get_widest_paths(), igraph_widest_path_widths_dijkstra() and igraph_widest_path_widths_floyd_warshall() to find widest paths (#1893, thanks to @Gomango999).
• igraph_graph_center() finds the central vertices of the graph. The central vertices are the ones having a minimum eccentricity (PR #2084, thanks to @pradkrish).
• igraph_graph_count() returns the number of unlabelled graphs on a given number of vertices. It is meant to find the maximum isoclass value.
• igraph_has_mutual() checks if a directed graph has any mutual edges.
• igraph_heap_clear() and igraph_heap_min_clear() remove all elements from an igraph_heap_t or an igraph_heap_min_t, respectively.
• igraph_invalidate_cache() invalidates all cached graph properties, forcing their recomputation next time they are requested. This function should not be needed in everyday usage, but may be useful in debugging and benchmarking.
• igraph_is_forest() to check whether a graph is a forest (#1888, thanks to @rohitt28).
• igraph_is_acyclic() to check whether a graph is acyclic (#1945, thanks to @borsgeorgica).
• igraph_is_perfect() to check whether a graph is a perfect graph (#1730, thanks to @guyroznb).
• igraph_hub_and_authority_scores() calculates the hub and authority scores of a graph as a matching pair.
• igraph_layout_umap() and igraph_layout_umap_3d() to lay out a graph in 2D or 3D space using the UMAP dimensionality reduction algorithm.
• igraph_local_scan_subset_ecount() counts the number of edges in induced sugraphs from a subset of vertices.
• igraph_matrix_view_from_vector() allows interpreting the data stored in a vector as a matrix of the specified size.
• igraph_minimum_cycle_basis() computes an unweighted minimum cycle basis (experimental).
• igraph_pseudo_diameter() and igraph_pseudo_diameter_dijkstra() to determine a lower bound for the diameter of a graph (unweighted or weighted).
• igraph_regular_tree() creates a regular tree where all internal vertices have the same total degree.
• igraph_rngtype_pcg32 and igraph_rngtype_pcg64 implement 32-bit and 64-bit variants of the PCG random number generator.
• igraph_rng_get_pois() generates random variates from the Poisson distribution.
• igraph_roots_for_tree_layout() computes a set of roots suitable for a nice tree layout.
• igraph_spanner() calculates a spanner of a graph with a given stretch factor (#1752, thanks to @guyroznb)
• igraph_sparse_adjacency() and igraph_sparse_weighted_adjacency() constructs graphs from (weighted) sparse matrices.
• igraph_sparsemat_get() to retrieve a single element of a sparse matrix.
• igraph_sparsemat_normalize_rows() and igraph_sparsemat_normalize_cols() to normalize sparse matrices row-wise or column-wise.
• igraph_stack_capacity() to query the capacity of a stack.
• igraph_strvector_capacity() returns the maximum number of strings that can be stored in a string vector without reallocating the memory block holding the pointers to the individual strings.
• igraph_strvector_merge() moves all strings from one string vectors to the end of another without re-allocating them.
• igraph_strvector_push_back_len() adds a new string to the end of a string vector and allows the user to specify the length of the string being added.
• igraph_strvector_reserve() reserves space for a given number of string pointers in a string vector.
• igraph_symmetric_tree() to create a tree with the specified number of branches at each level (#1859, thanks to @YuliYudith and @DoruntinaM).
• igraph_trussness() calculates the trussness of each edge in the graph (#1034, thanks to @alexperrone)
• igraph_turan() generates Turán graphs (#2088, thanks to @pradkrish)
• igraph_vector_all_almost_e(), igraph_vector_complex_all_almost_e(), igraph_matrix_all_almost_e(), igraph_matrix_complex_all_almost_e() for elementwise comparisons of floating point vector and matrices with a relative tolerance.
• igraph_vector_complex_zapsmall() and igraph_matrix_complex_zapsmall() for replacing small components of complex vector or matrix elements with exact zeros.
• igraph_vector_lex_cmp_untyped() and igraph_vector_colex_cmp_untyped() for lexicographic and colexicographic comparison of vectors, similarly to igraph_vector_lex_cmp() and igraph_vector_colex_cmp(). The difference between the two variants is that the untyped versions declare the vectors as const void*, making the functions suitable as comparators for qsort().
• igraph_vector_permute() functions to permute a vector based on an index vector.
• igraph_vector_ptr_sort_ind() to obtain an index vector that would sort a vector of pointers based on some comparison function.
• igraph_vector_range() to fill an existing vector with a range of increasing numbers.
• igraph_vector_remove_fast() functions to remove an item from a vector by swapping it with the last element and then popping it off. It allows one to remove an item from a vector in constant time if the order of items does not matter.
• igraph_vertex_path_from_edge_path() converts a sequence of edge IDs representing a path to an equivalent sequence of vertex IDs that represent the vertices the path travelled through.
• igraph_vs_range(), igraph_vss_range(), igraph_es_range() and igraph_ess_range() creates vertex and edge sequences from C-style intervals (closed from the left, open from the right).
• igraph_wheel() to create a wheel graph (#1938, thanks to @kwofach).

Removed

• igraph_adjlist_remove_duplicate(), igraph_betweenness_estimate(), igraph_closeness_estimate(), igraph_edge_betweenness_estimate(), igraph_inclist_remove_duplicate(), igraph_is_degree_sequence() and igraph_is_graphical_degree_sequence() were deprecated earlier in 0.9.0 and are now removed in this release.
• igraph_dnorm(), igraph_strvector_move_interval(), igraph_strvector_permdelete() and igraph_strvector_remove_negidx() were removed. These are not breaking changes as the functions were never documented, they were only exposed from one of the headers.
• igraph_eigen_laplacian(), igraph_es_fromto() and igraph_maximum_matching() were removed. These are not breaking changes either as the functions were never implemented, they returned an error code unconditionally.

Changed

• igraph_degree_sequence_game() now supports an additional method, IGRAPH_DEGSEQ_EDGE_SWITCHING_SIMPLE, an edge-switching MCMC sampler.
• igraph_get_adjacency() and igraph_get_adjacency_sparse() now count loop edges twice in undirected graphs when using IGRAPH_GET_ADJACENCY_BOTH. This is to ensure consistency with IGRAPH_GET_ADJACENCY_UPPER and IGRAPH_GET_ADJACENCY_LOWER such that the sum of the upper and the lower triangle matrix is equal to the full adjacency matrix even in the presence of loop edges.
• igraph_matrix_print() and igraph_matrix_fprint() functions now align columns when priting.
• igraph_read_graph_gml() now supports graph attributes (in addition to vertex and edge attributes).
• igraph_read_graph_gml() now uses NaN as the default numerical attribute values instead of 0.
• The Pajek parser in igraph_read_graph_pajek() is now less strict and accepts more files.
• igraph_ring() no longer simplifies its result when generating a one- or two-vertex graph. The one-cycle has a self-loop and the undirected two-cycle has parallel edges.
• igraph_vector_view() now allows data to be NULL in the special case when length == 0.
• igraph_version() no longer returns an error code.
• igraph_write_graph_gml() uses the creator parameter in a different way: the supplied string is now written into the Creator line as-is instead of being appended to a default value.
• igraph_write_graph_gml() skips writing NaN values. These two changes ensure consistent round-tripping.
• igraph_write_graph_gml() and igraph_read_graph_gml() now have limited support for entity encoding.
• igraph_write_graph_ncol() now preserves the edge ordering of the graph when writing an NCOL file.
• igraph functions that take an ARPACK options object now also accept NULL in place of an options object, and they will fall back to using a default object provided by igraph_arpack_options_get_default().
• Foreign format readers now present more informative error messages.
• The default tolerance of the zapsmall functions is now eps^(2/3) instead of eps^(1/2) where eps is the machine epsilon of igraph_real_t.
• It is now possible to override the uniform integer and the Poisson samplers in the random number generator interface.

Fixed

• When an error occurs during parsing DL, GML, NCOL, LGL or Pajek files, line numbers are now reported correctly.
• The GraphML parser does not print to stderr any more in case of encoding errors and other error conditions originating from the underlying libxml2 library.
• The GraphML parser would omit some edges and vertices when reading files with custom attribute types, such as those produced by yEd. This is now corrected.
• The GML parser no longer mixes up Inf and NaN and -Inf now works.
• The GML parser now supports nodes with no id field.
• The GML parser now performs more stringent checks on the input file, such as verifying that id, source, target and directed fields are not duplicated.
• The core data structures (vector, etc.) have overflow checks now.
• Deterministic graph generators, as well as most random ones, have overflow checks now.
• Graphs no longer lose all their attributes after calling igraph_contract_vertices().
• igraph_hrg_init() does not throw an assertion error anymore for zero vertices.
• igraph_matrix_complex_create() and igraph_matrix_complex_create_polar() now set their sizes correctly.
• igraph_random_walk() took one fewer steps than specified.
• igraph_sparsemat_getelements_sorted() did not sort the elements for triplet matrices correctly; this is fixed now.
• igraph_write_graph_gml() no longer produces corrupt output when some string attribute values contain " characters.

Deprecated

• igraph_clusters() has been renamed to igraph_connected_components(); the old name is deprecated and will be removed in 0.11.
• igraph_complex_eq_tol() is now deprecated in favour of igraph_complex_almost_equals().
• igraph_get_sparsemat() is deprecated in favour of igraph_get_adjacency_sparse(), and will be removed in 0.11. Note that igraph_get_adjacency_sparse() takes an initialized sparse matrix as input, unlike igraph_get_sparsemat() which takes an uninitialized one.
• igraph_get_stochastic_sparsemat() is deprecated in favour of igraph_get_stochastic_sparse(), and will be removed in 0.11. Note that igraph_get_stochastic_sparse() takes an initialized sparse matrix as input, unlike igraph_get_stochastic_sparsemat(), which takes an uninitialized one.
• igraph_isomorphic_34() has been deprecated in favour of igraph_isomorphic(). Note that igraph_isomorphic() calls an optimized version for directed graphs of size 3 and 4, and undirected graphs with 3-6 vertices, so there is no need for a separate function.
• igraph_laplacian() is now deprecated; use igraph_get_laplacian() or igraph_get_laplacian_sparse() depending on whether you need a dense or a sparse matrix.
• igraph_lattice() has been renamed to igraph_square_lattice() to indicate that this function generates square lattices only. The old name is deprecated and will either be removed in 0.11 or will be changed to become a generic lattice generator that also supports other types of lattices.
• igraph_local_scan_neighborhood_ecount() is now deprecated in favour of igraph_local_scan_subset_ecount().
• igraph_matrix_all_e_tol() is now deprecated in favour of igraph_matrix_all_almost_e().
• igraph_matrix_copy() is now deprecated; use igraph_matrix_init_copy() instead. The new name emphasizes that the function initializes the first argument instead of expecting an already-initialized target matrix. The old name will be removed in 0.11.
• igraph_matrix_e() and igraph_matrix_e_ptr() have been renamed to igraph_matrix_get() and igraph_matrix_get_ptr(). The old names are deprecated and will be removed in 0.11.
• igraph_random_edge_walk() has been deprecated by igraph_random_walk() to support edges and/or vertices for the random walk in a single function. It will be removed in 0.11.
• igraph_read_graph_dimacs() has been renamed to igraph_read_graph_dimacs_flow(); the old name is deprecated and might be re-used as a generic DIMACS reader in the future. Also, the function now uses igraph_integer_t as the source and target vertex IDs instead of a long int.
• igraph_shortest_paths() and related functions were renamed to igraph_distances(); the old name was unfortunate because these functions calculated path lengths only and not the paths themselves. The old names are deprecated and will be removed in 0.11.
• igraph_sparsemat_copy(), igraph_sparsemat_diag() and igraph_sparsemat_eye() have been renamed to igraph_sparsemat_init_copy(), igraph_sparsemat_init_diag() and igraph_sparsemat_init_eye() to indicate that they initialize a new sparse matrix. The old names are deprecated and will be removed in 0.11.
• igraph_strvector_add() has been renamed to igraph_strvector_push_back() for sake of consistency with other vector-like data structures; the old name is deprecated and will be removed in 0.11.
• igraph_strvector_copy() has been renamed to igraph_strvector_init_copy() for sake of consistency with other vector-like data structures; the old name is deprecated and will be removed in 0.11.
• igraph_strvector_get() now returns a const char* and not a char* to indicate that you are not supposed to modify the string in the vector directly. If you do want to modify it and you are aware of the implications (i.e. the new string must not be longer than the original one), you can cast away the constness of the return value before modifying it.
• igraph_strvector_set2() has been renamed to igraph_strvector_set_len(); the old name is deprecated and will be removed in 0.11.
• igraph_tree() has been renamed to igraph_kary_tree(); the old name is deprecated and will be removed in 0.11.
• igraph_vector_e() and igraph_vector_e_ptr() have been renamed to igraph_vector_get() and igraph_vector_get_ptr(). The old names are deprecated and will be removed in 0.11.
• igraph_vector_e_tol() is now deprecated in favour of igraph_vector_all_almost_e().
• igraph_vector_copy() is now deprecated; use igraph_vector_init_copy() instead. The new name emphasizes that the function initializes the first argument instead of expecting an already-initialized target vector. The old name will be removed in 0.11.
• igraph_vector_init_seq() is now deprecated in favour of igraph_vector_init_range(), which uses C-style intervals (closed from the left and open from the right).
• igraph_vs_seq(), igraph_vss_seq(), igraph_es_seq() and igraph_ess_seq() are now deprecated in favour of igraph_vs_range(), igraph_vss_range(), igraph_es_range() and igraph_ess_range() because these use C-style intervals (closed from the left, open from the right).
• igraph_write_graph_dimacs() has been renamed to igraph_write_graph_dimacs_flow(); the old name is deprecated and might be re-used as a generic DIMACS writer in the future. Also, the function now uses igraph_integer_t as the source and target vertex IDs instead of a long int.
• igraph_zeroin() is deprecated and will be removed in 0.11, with no replacement. The function is not graph-related and was never part of the public API.
• The macros igraph_Calloc, igraph_Realloc and igraph_Free have been deprecated in favour of IGRAPH_CALLOC, IGRAPH_REALLOC and IGRAPH_FREE to simplify the API. The deprecated variants will be removed in 0.11.

Other

• Documentation improvements.
• Support for Intel's LLVM-based compiler.