igraph

This is the first release candidate of the upcoming 1.0.0 igraph release. Some API changes are still expected in the next few days. The changelog posted here is merged from the changelogs of the master and develop branches, and it represents all the changes compared to the latest stable release (0.10.16). These changes will be repeated in the changelog of 1.0.0 when we are ready.

Breaking changes

This section gives detailed on breaking changes you need to consider when updating code written for igraph 0.10.x.

General changes

• igraph now requires a C++ compiler that supports the C++14 standard.
• igraph_setup() is now recommended to be called before using the library. This function may gain essential functions in the future. See below for details.
• igraph_integer_t was renamed to igraph_int_t, but igraph_integer_t is kept as an alias and it will remain available for at least the next major version. Library headers and source code uses igraph_int_t from now on.
• igraph_rng_set_default() now returns a pointer to the previous RNG. Furthermore, this function now only stores a pointer to the igraph_rng_t struct passed to it, instead of copying the struct. Thus the igraph_rng_t must continue to exist for as long as it is used as the default RNG.
• Interruption handlers do not take a void* argument any more; this is relevant to maintainers of higher-level interfaces only.
• Interruption handlers now return an igraph_bool_t instead of an igraph_error_t; the returned value must be true if the calculation has to be interrupted and false otherwise.
• igraph_status(), igraph_statusf() and their macro versions (IGRAPH_STATUS() and IGRAPH_STATUSF()) do not convert error codes to IGRAPH_INTERRUPTED any more. Any error code returned from the status handler function is forwarded intact to the caller. If you want to trigger the interruption of the current calculation from the status handler without reporting an error, report IGRAPH_INTERRUPTED explicitly. It is the responsibility of higher-level interfaces to handle this error code appropriately.
• The RNG_BEGIN() and RNG_END() macros were removed. You are now responsible for seeding the RNG before using any igraph function that may use random numbers by calling igraph_rng_seed(igraph_rng_default(), ...), or by simply ensuring that igraph_setup() was called before the first use of the library.

Error codes

• The IGRAPH_EINVEVECTOR error code was removed; igraph_create() and igraph_add_edges() that used to return this error code for invalid edge vectors will now return IGRAPH_EINVAL instead.
• The IGRAPH_NONSQUARE error code was removed; functions that used this error code now return IGRAPH_EINVAL instead when encountering a non-square matrix.
• The IGRAPH_EGLP error code and all other GLP-specific error codes (starting with IGRAPH_GLP_) were removed; functions that used this error code now return IGRAPH_FAILURE instead, providing more details in the message associated to the error code.
• The IGRAPH_ELAPACK error code was removed; functions that used this error code now return IGRAPH_FAILURE instead, providing more details in the message associated to the error code.
• The IGRAPH_CPUTIME error code was removed in favour of the interruption mechanism built into igraph.
• The unused IGRAPH_EDIVZERO and IGRAPH_EATTRIBUTES error codes were removed with no replacement.
• The deprecated error code IGRAPH_ENEGLOOP was removed. Use IGRAPH_ENEGCYCLE instead. The underlying numerical value is the same as it was for IGRAPH_ENEGLOOP.
• ARPACK-specific error codes (starting with IGRAPH_ARPACK_...) were replaced with a single IGRAPH_EARPACK error code. Details about the underlying ARPACK failure are provided in the error message.
• A new error code called IGRAPH_EINVEID was added for cases when an invalid edge ID was encountered in an edge ID vector.

Core data structures

• igraph_strvector_push_back_len() now takes a length parameter of size_t instead of igraph_integer_t.
• igraph_strvector_print() no longer takes a file parameter. Use igraph_strvector_fprint() to print to a file.
• igraph_vector_reverse() no longer returns an error code.
• igraph_vector_shuffle() no longer returns an error code.
• igraph_vector_swap() and igraph_matrix_swap() no longer return an error code.
• igraph_vector_list_swap() and igraph_graph_list_swap() no longer return an error code.
• igraph_vector_swap_elements() no longer returns an error code.
• igraph_vector_list_swap_elements() and igraph_graph_list_swap_elements() no longer return an error code.
• igraph_matrix_copy_to() gained an igraph_matrix_storage_t storage parameter that specifies whether the data should be written in column-major or row-major format.

Attribute handling

• igraph_attribute_handler_t members that formerly took an untyped igraph_vector_ptr_t argument are now taking a typed igraph_attribute_record_list_t argument instead.
• The deprecated IGRAPH_ATTRIBUTE_DEFAULT value of the igraph_attribute_type_t enum was removed.
• The gettype member of igraph_attribute_table_t was renamed to get_type for sake of consistency with the naming scheme of other struct members.
• Attribute table members that retrieve graph, vertex or edge attributes must not clear the incoming result vector any more; results must be appended to the end of the provided result vector instead.
• The value member of igraph_attribute_record_t is now a union that can be used to formally treat the associated pointer as an igraph_vector_t *, igraph_strvector_t * or igraph_vector_bool_t *.

Core graph manipulation

• igraph_delete_vertices_map() (formerly called igraph_delete_vertices_idx()) and igraph_induced_subgraph_map() now use -1 to represent unmapped vertices in the returned forward mapping vector and they do not offset vertex indices by 1 any more. (Note that the inverse map always behaved this way, this change makes the two mappings consistent).
• igraph_edges() gained a new bycol argument that determines the order in which the edges are returned. bycol = false reproduces the existing behaviour, while bycol = true returns the edges suitable for a matrix stored in column-wise order.
• igraph_neighbors() and igraph_vs_adj() gained two extra arguments to specify what to do with loop and multiple edges. This makes their interfaces consistent with igraph_adjlist_init().
• igraph_incident() and igraph_es_incident() gained an extra arguments to specify what to do with loop edges. This makes their interfaces consistent with igraph_inclist_init().
• igraph_multiple_t was removed from the public API as it is essentially a boolean. The symbolic constants IGRAPH_MULTIPLE and IGRAPH_NO_MULTIPLE were kept to improve readability of code written directly in C.

Basic graph properties

• igraph_density() now takes an optional weights parameter.
• igraph_is_simple() gained an extra igraph_bool_t argument that decides whether edge directions should be considered. Directed graphs with a mutual edge pair are treated as non-simple if this argument is set to IGRAPH_UNDIRECTED (which treats the graph as if it was undirected).
• The type of the loops argument of igraph_adjlist_init_complementer(), igraph_centralization_degree(), igraph_centralization_degree_tmax(), igraph_degree(), igraph_maxdegree(), igraph_sort_vertex_ids_by_degree() and igraph_strength() was changed to igraph_loops_t from igraph_bool_t, allowing finer-grained control about how loop edges are treated.
• igraph_get_biadjacency() now takes a weights parameter, and can optionally create weighted biadjacency matrices.
• igraph_adjacency() now treats IGRAPH_LOOPS_TWICE as IGRAPH_LOOPS_ONCE when the mode is IGRAPH_ADJ_DIRECTED, IGRAPH_ADJ_UPPER or IGRAPH_ADJ_LOWER. For directed graphs, this is for the sake of consistency with the rest of the library where IGRAPH_LOOPS_TWICE is considered for undirected graphs only. For the "upper" and "lower" modes, double-counting the diagonal makes no sense because the double-counting artifact appears when you add the transpose of an upper (or lower) diagonal matrix on top of the matrix itself. See Github issue #2501 for more context.

Graph generators

• igraph_barabasi_game(), igraph_barabasi_aging_game(), igraph_recent_degree_game() and igraph_recent_degree_aging_game() no longer interprets an empty outseq vector as a missing out-degree sequence. Pass NULL if you don't wish to specify an out-degree sequence.
• igraph_degree_sequence_game() no longer interprets an empty in-degree vector as a request for generating undirected graphs. To generate undirected graphs, pass NULL for in-degrees.
• igraph_lcf() was renamed to igraph_lcf_small() and igraph_lcf_vector() was renamed to igraph_lcf(). Now igraph_lcf() takes shifts as a vector input, while igraph_lcf_small() accepts a shorthand notation where shifts are given as a variable number of function arguments.
• igraph_sbm_game() uses an igraph_edge_type_sw_t allowed_edge_types parameter instead of igraph_bool_t loops and supports generating graphs with mutli-edges. The parameter determining the total number of vertices (n) was removed as it was redundant.
• igraph_rewire_edges() uses an igraph_edge_type_sw_t allowed_edge_types parameter instead of loops and multiple.
• igraph_watts_strogatz_game() uses an igraph_edge_type_sw_t allowed_edge_types parameter instead of loops and multiple.
• igraph_static_fitness_game() uses an igraph_edge_type_sw_t allowed_edge_types parameter instead of loops and multiple.
• igraph_static_power_law_game() uses an igraph_edge_type_sw_t allowed_edge_types parameter instead of loops and multiple.

Shortest paths

• igraph_distances(), igraph_distances_cutoff(), igraph_get_shortest_path(), igraph_get_shortest_paths() and igraph_get_all_shortest_paths() gained a weights argument. The functions now automatically select the appropriate implementation (unweighted, Dijkstra, Bellman-Ford or Johnson) algorithm based on whether weights are present and whether there are negative weights or not. You can still call the individual methods by their more specific names.
• igraph_distances_johnson() now takes a mode parameter to determine in which direction paths should be followed.
• igraph_similarity_jaccard() and igraph_similarity_dice() now take two sets of vertices to create vertex pairs of, instead of one.
• The weighted variants of igraph_diameter(), igraph_pseudo_diameter(), igraph_radius(), igraph_graph_center(), igraph_eccentricity() and igraph_average_path_length() were merged into the undirected ones by adding a new argument named weights in the second position.
• The weights parameter of igraph_average_path_length(), igraph_global_efficiency(), igraph_local_efficiency() and igraph_average_local_efficiency() were moved to the second position, after the graph itself, for sake of consistency with other functions.
• igraph_get_all_simple_paths() returns its results in an integer vector list (igraph_vector_int_list_t) instead of a single integer vector.
• igraph_get_all_simple_paths() now has an additional parameter that allows restricting paths by minimum length as well.

Community detection

• igraph_community_edge_betweenness() now takes both a weights and a lengths parameter. Egde weights (interpreted as connection strengths) are used to divide betweenness scores before selecting them for removal as well as for the modularity computation. Edge lengths are used for defining shortest path lengths during the betweenness computation. This fixes issues #2229 and #1040.
• igraph_community_infomap() now supports regularization and gained the is_regularized and regularization_strength parameters.
• igraph_community_label_propagation() changed signature to allow specification of label propagation algorithm (LPA) variants. A new fast label propagation variant was added.
• igraph_community_leiden() now takes two vertex_out_weights and vertex_in_weights parameters in order to support directed graphs, instead of the previous single node_weights parameter. To obtain the old behavior for undirected graphs, pass the vertex weights as vertex_out_weights and set vertex_in_weights to NULL.
• The history parameter of igraph_community_leading_eigenvector() is now a pointer to an igraph_vector_int_t instead of an igraph_vector_t.
• igraph_community_optimal_modularity() now takes a resolution parameter and its weight parameter was moved to the second place.
• igraph_community_spinglass_single() now uses igraph_real_t for its inner_links and outer_links output parameters, as these return not simply edge counts, but the sum of the weights of some edges.

Isomorphism functions and permutations

• igraph_count_automorphisms() has been renamed to igraph_count_automorphisms_bliss() because it has a BLISS-specific interface. A new igraph_count_automorphisms() function was added with a simplified interface that does not depend on BLISS.
• igraph_automorphism_group() has been renamed to igraph_automorphism_group_bliss() because it has a BLISS-specific interface. A new igraph_automorphism_group() function was added with a simplified interface that does not depend on BLISS.
• igraph_canonical_permutation() has been renamed to igraph_canonical_permutation_bliss() because it has a BLISS-specific interface. A new igraph_canonical_permutation() function was added with a simplified interface that does not depend on BLISS.
• igraph_subisomorphic_lad() does not have a CPU time limit parameter any more. If you wish to stop the calculation from another thread or a higher level interface, use igraph's interruption mechanism.
• The semantics of the igraph_permute_vertices() permutation argument has changed: the i-th element of the vector now contains the index of the original vertex that will be mapped to the i-th vertex in the new graph. This is now consistent with how other igraph functions treat permutations and vertex index vectors; for instance, you can now pass the result of igraph_topological_sorting() directly to igraph_permute_vertices() to obtain a new graph where the vertices are sorted topologically.
• As a consequence to the change in the semantics of the igraph_permute_vertices() permutation argument, the semantics of the permutations returned from igraph_canonical_permutation() and igraph_canonical_permutation_bliss() have also been inverted to maintain the invariant that the output of these functions can be fed into igraph_permute_vertices() directly.

Centralities

• All betweenness functions got normalized parameter to support normalizing the result by the number of vertex pairs in the graph. At the same time, parameter ordering was standardized. The following functions are affected: igraph_betweenness(), igraph_betweenness_cutoff(), igraph_edge_betweenness(), igraph_edge_betweenness_cutoff(), igraph_betweenness_subset(), igraph_edge_betweenness_subset().
• igraph_edge_betweenness() and igraph_edge_betweenness_cutoff() now have an eids parameter to return only a subset of results. This makes their interface consistent with other betweenness functions.
• igraph_eigenvector_centrality(), igraph_centralization_eigenvector_centrality() and igraph_centralization_eigenvector_centrality_tmax() now use a mode parameter with possible values IGRAPH_OUT, IGRAPH_IN or IGRAPH_ALL to control how edge directions are considered. Previously they used a boolean directed parameter.
• igraph_eigenvector_centrality(), igraph_centralization_eigenvector_centrality() and igraph_centralization_eigenvector_centrality_tmax() no longer have a scale parameter. The result is now always scaled so that the largest centrality value is 1.
• igraph_hub_and_authority_scores() no longer has a scale parameter. The result is now always scaled so that the largest hub and authority scores are each 1.
• igraph_pagerank(), igraph_personalized_pagerank() and igraph_personalized_pagerank_vs() had their parameter ordering standardized.

Layouts

• igraph_layout_sugiyama() does not return an "extended graph" any more. The bends in the edges of the layout are encoded in a list of matrices instead; each item in the list belongs to an edge of the original graph and contains the control points of the edge in a row-wise fashion. The matrix will have no rows if no control points are needed on the edge.

Other network analysis

• igraph_minimum_spanning_tree() takes a new method parameter that controls the algorithm used for finding the spanning tree. Kruskal's algorithm was added.
• The deprecated igraph_rng_get_dirichlet() function was removed.
• igraph_motifs_randesu_no() and igraph_motifs_randesu_estimate() now take an igraph_real_t as their result argument to prevent overflows when igraph is compiled with 32-bit integers.
• The experimental functions igraph_fundamental_cycles() and igraph_minimum_cycle_basis() now use the type igraph_real_t for their bfs_cutoff parameter, and had their weights parameter moved to the 2nd position.
• igraph_rewire() now takes an igraph_edge_type_sw_t parameter to specify whether to create self-loops. The igraph_rewiring_t enum type was removed. Instead of the old IGRAPH_REWIRING_SIMPLE, use IGRAPH_SIMPLE_SW. Instead of the old IGRAPH_REWIRING_SIMPLE_LOOPS, use IGRAPH_LOOPS_SW.

Foreign formats

• igraph_read_graph_ncol() and igraph_read_graph_lgl() now uses a default edge weight of 1 instead of 0 for files that do not contain edge weights for at least some of the edges.

Added

• igraph_setup() performs all initialization tasks that are recommended before using the igraph library. Right now this function only initializes igraph's internal random number generator with a practically random seed, but it may also perform other tasks in the future. It is recommended to call this function before using any other function from the library (although most of the functions will work fine now even if this function is not called).
• igraph_erdos_renyi_game_gnm() gained a multiple Boolean argument to uniformly sample G(n,m) graphs with multi-edges.
• igraph_bipartite_game_gnm() gained a multiple Boolean argument to uniformly sample bipartite G(n,m) graphs with multi-edges.
• igraph_iea_game() samples random multigraphs through independent edge assignment.
• igraph_bipartite_iea_game() samples random bipartite multigraph through independent edge assignment.
• igraph_weighted_biadjacency() creates a weighted graph from a bipartite adjacency matrix.
• igraph_vector_ptr_capacity() returns the allocated capacity of a pointer vector.
• igraph_vector_ptr_resize_min() deallocates unused capacity of a pointer vector.
• igraph_strvector_fprint() prints a string vector to a file.
• igraph_rng_sample_dirichlet(), igraph_rng_sample_sphere_volume() and igraph_rng_sample_sphere_surface() samples vectors from a Dirichlet distribution or from the volume or surface of a sphere while allowing the user to specify the random number generator to use.
• igraph_nearest_neighbor_graph() computes a neighborhood graph of spatial points based on a neighbor count, cutoff distance, and chosen metric (experimental function). Thanks to Arnór Friðriksson @Zepeacedust for implementing this in #2788!
• igraph_delaunay_graph() computes a Delaunay graph of a spatial point set (experimental function). Thanks to Arnór Friðriksson @Zepeacedust for implementing this in #2806!
• igraph_spatial_edge_lengths() computes edges lengths based on spatial vertex coordinates (experimental function).
• igraph_community_leiden_simple() is a simplified interface to igraph_community_leiden() that allows selecting the objective function to maximize directly.
• igraph_vector_difference_and_intersection_sorted() calculates the intersection and the differences of two vectors simultaneously.
• igraph_layout_align() attempts to align a graph layout with the coordinate axes in a visually pleasing manner (experimental function).
• igraph_product() supports the lexicographic, strong and modular graph products. Thanks to Gulshan Kumar @gulshan-123 for contributing this functionality in #2772 and #2793!
• igraph_rooted_product() computes the the rooted graph product. Thanks to Gulshan Kumar @gulshan-123 for contributing this functionality in #2793!
• igraph_mycielskian() and igraph_mycielski_graph() compute a Mycielski transformation of a graph, and a Mycielski graph, respectively. Thanks to Gulshan Kumar @gulshan-123 for contributing this functionality in #2741!
• igraph_path_graph() is a convenience wrapper for igraph_ring() with circular=false.
• igraph_cycle_graph() is a convenience wrapper for igraph_ring() with circular=true.
• igraph_bond_percolation(), igraph_site_percolation() and igraph_edgelist_percolation() calculates the time evolution of the size of the giant component of a graph when edges or vertices are added one by one in a certain (or random) order. Thanks to Arnór Friðriksson @Zepeacedust for implementing this in #2778!
• igraph_invert_permutation() inverts a permutation stored in an integer vector.
• igraph_is_vertex_coloring() and igraph_is_edge_coloring() check if a vertex or edge coloring is valid, i.e. whether adjacenct vertices/edges always have distinct colors. Thanks to Sarah Rashidi @its-serah for contributing this in #2807!
• igraph_rich_club_sequence() calculates how the density of a graph changes as vertices are removed. Thanks to Zara Zong @minifinity for contributing this in #2740!

Changed

• The Pajek format reader and writer now map vertex labels to the name vertex attribute in igraph. The id attribute is no longer used.
• igraph_minimum_size_separators() no longer returns any separating vertex sets for complete graphs. Prior to igraph 1.0, it would return all n - 1 size vertex subsets where n is the vertex count.
• igraph_community_edge_betweenness() now treats edges with large weights as strong connections.
• igraph_biadjacency() now truncates non-integer matrix entries to their integer part instead of rounding them up. This brings consistency with related functions such as igraph_adjacency().
• The order of edges in the graph returned by igraph_(weighted_)adjacency() and igraph_biadjacency() has changed. Note that these functions do not guarantee any specific edge order.
• igraph_eigenvector_centrality() now warns about eigenvector centralities equal to zero, as these indicate a disconnected graph, for which eigenvector centrality is not meaningful.
• igraph_hub_and_authority_scores() now warns when a large fraction of centrality scores are zero, as this indicates a non-unique solution, and thus the returned result may not be meaningful.
• igraph_hub_and_authority_scores() now warns when providing an undirected graph as input, and falls back to the equivalent eigenvector centrality computation.
• igraph_get_stochastic_sparse() no longer throws an error when some row or column sums are zero. This brings its behaviour in line with igraph_get_stochastic().
• igraph_vector_append(), igraph_strvector_append() and igraph_vector_ptr_append() now use a different allocation strategy: if the to vector has insufficient capacity, they double its capacity. Previously they reserved precisely as much capacity as needed for appending the from vector.
• The implementation of the Infomap algorithm behind igraph_community_infomap() has been updated with a more recent version (2.8.0). Isolated vertices are now supported.
• igraph_vector_difference_sorted() now handles multisets properly (and documents how the multiplicities are handled).
• igraph_bipartite_game_gnp() can now generate graphs with more than a hundred million vertices. Thanks to Dev Lohani @devlohani99 for implementing this in #2767!
• igraph_reindex_membership() now supports arbitrary cluster indices. Previously, it would error when indices are not within 0 .. n-1 where n is the membership vector length.
• igraph_modularity() now supports arbitrary cluster indices. However, ensuring that cluster indices are within the range 0 .. n-1, where n is the vertex count, allows for better performance.

Finalized experimental functions

• The following functions are not experimental any more: igraph_count_loops(), igraph_count_reachable(), igraph_degree_correlation_vector, igraph_distances_cutoff(), igraph_distances_floyd_warshall(), igraph_distances_dijkstra_cutoff(), igraph_ecc(), igraph_enter_safelocale(), igraph_exit_safelocale(), igraph_feedback_vertex_set(), igraph_find_cycle(), igraph_get_shortest_path_astar(), igraph_graph_power(), igraph_hexagonal_lattice(), igraph_hypercube(), igraph_is_bipartite_coloring(), igraph_is_clique(), igraph_is_complete(), igraph_is_edge_coloring(), igraph_is_vertex_coloring(), igraph_is_independent_vertex_set(), igraph_join(),igraph_joint_degree_distribution(), igraph_joint_degree_matrix(), igraph_joint_type_distribution(), igraph_layout_align(), igraph_layout_merge_dla(), igraph_mean_degree(), igraph_radius(), igraph_realize_bipartite_degree_sequence(), igraph_reachability(), igraph_transitive_closure(), igraph_tree_from_parent_vector(), igraph_triangular_lattice(), igraph_vector_intersection_size_sorted(), igraph_voronoi().

Fixed

• igraph_community_spinglass_single() now uses igraph_real_t for its inner_links and outer_links output parameters, as these return not simply edge counts, but the sum of the weights of some edges. Thus these results are no longer incorrectly rounded.
• Fix failure in SIR simulation due to roundoff errors creating slightly negative rates.
• Fix infinite coordinates for certain path graphs with igraph_layout_kamada_kawai_3d().
• igraph_community_leiden() did not iterate until the partition ceased to change when n_iterations < 0. Thanks to Lucas Lopes Felipe @lucaslopes for fixing this in #2799!
• The widest path functions igraph_widest_path_widths_floyd_warshall(), igraph_widest_path_widths_dijkstra(), igraph_get_widest_paths(), and igraph_get_widest_path() incorrectly ignored edges with positive infinite width. Now they ignore edges with negative infinite width.

Removed

• Removed igraph_Calloc(), igraph_Realloc() and igraph_Free(). Use IGRAPH_CALLOC(), IGRAPH_REALLOC() and IGRAPH_FREE() instead.
• The deprecated igraph_adjacent_triangles() was removed. Use igraph_count_adjacent_triangles() instead.
• The deprecated igraph_are_connected() was removed. Use igraph_are_adjacent() instead.
• The deprecated igraph_automorphisms() was removed. Use igraph_count_automorphisms() or igraph_count_automorphisms_bliss() instead.
• The deprecated igraph_convex_hull() was removed. Use igraph_convex_hull_2d() instead.
• The deprecated igraph_decompose_destroy() was removed.
• The deprecated igraph_hub_score() and igraph_authority_score() were removed.
• The deprecated igraph_vs_seq(), igraph_vss_seq(), igraph_es_seq(), igraph_ess_range(), and igraph_vector_init_seq() were removed. Use the range alternatives instead of the old seq ones.
• The deprecated igraph_erdos_renyi_game() and igraph_bipartite_game() were removed. Use the corresponding functions with _gnm() and _gnp() in the name instead.
• The deprecated igraph_tree() was removed. Use igraph_kary_tree() instead.
• The deprecated igraph_lattice() was removed. Use igraph_square_lattice() instead.
• The deprecated igraph_minimum_spanning_tree_prim() was removed. Use igraph_minimum_spanning_tree() in conjunction with igraph_subgraph_from_edges() instead.
• The deprecated igraph_minimum_spanning_tree_unweighted() was removed. Use igraph_minimum_spanning_tree() in conjunction with igraph_subgraph_from_edges() instead.
• The deprecated igraph_get_sparsemat() was removed. Use igraph_get_adjacency_sparse() instead.
• The deprecated igraph_get_stochastic_sparsemat() was removed. Use igraph_get_stochastic_sparse() instead.
• The deprecated igraph_laplacian() was removed. Use igraph_get_laplacian() or igraph_get_laplacian_sparse() instead.
• The deprecated igraph_subgraph_edges() was removed. Use igraph_subgraph_from_edges() instead.
• The deprecated igraph_read_graph_dimacs() and igraph_write_graph_dimacs() were removed. These names may be re-used in the future. Use igraph_read_graph_dimacs_flow() and igraph_write_graph_dimacs_flow() instead.
• The deprecated igraph_isomorphic_function_vf2() was removed. Use igraph_get_isomorphisms_vf2_callback() instead.
• The deprecated igraph_subisomorphic_function_vf2() was removed. Use igraph_get_subisomorphisms_vf2_callback() instead.
• The deprecated igraph_isomorphic_34() was removed. Its functionality is accessible through igraph_isomorphic().
• The deprecated igraph_transitive_closure_dag() was removed. Use igraph_transitive_closure() instead, which works for all graphs, not just DAGs.
• The deprecated igraph_sparsemat_copy() was removed. Use igraph_sparsemat_init_copy() instead.
• The deprecated igraph_sparsemat_eye() was removed. Use igraph_sparsemat_init_eye() instead.
• The deprecated igraph_sparsemat_diag() was removed. Use igraph_sparsemat_init_diag() instead.
• The deprecated igraph_sparsemat() and igraph_weighted_sparsemat() functions were removed; use igraph_get_adjacency_sparse() instead.
• The deprecated igraph_random_edge_walk() was removed. Its functionality is incorporated in igraph_random_walk().
• The deprecated igraph_vector_qsort_ind() was removed. Use igraph_vector_sort_ind() instead.
• The deprecated igraph_vector_binsearch2() was removed. Use igraph_vector_contains_sorted() instead.
• The deprecated igraph_vector_copy() and igraph_matrix_copy() were removed. Use igraph_vector_init_copy() and igraph_matrix_init_copy() instead.
• The deprecated igraph_vector_e(), igraph_vector_e_ptr(), igraph_matrix_e() and igraph_matrix_e_ptr() were removed. Use the alternatives ending in _get() and _get_ptr() instead.
• The deprecated igraph_vector_move_interval2() was removed.
• The deprecated igraph_zeroin() was removed.
• The deprecated igraph_deterministic_optimal_imitation(), igraph_moran_process(), igraph_roulette_wheel_imitation() and igraph_stochastic_imitation() functions were removed.
• igraph_sample_dirichlet(), igraph_sample_sphere_surface() and igraph_sample_sphere_volume() were removed in favour of igraph_rng_sample_dirichlet(), igraph_rng_sample_sphere_surface() and igraph_rng_sample_sphere_volume(), which allow the user to specify the random number generator to use.
• The unused enum type igraph_fileformat_type_t was removed.
• The macros IGRAPH_POSINFINITY and IGRAPH_NEGINFINITY were removed. Use IGRAPH_INFINITY and -IGRAPH_INFINITY instead.

Deprecated

• igraph_delete_vertices_idx() is now deprecated in favour of igraph_delete_vertices_map(), which is functionally equivalent but has a name that is consistent with igraph_induced_subgraph_map().

Other

• Documentation improvements.
• Improved performance when creating graphs from dense adjacency matrices (igraph_adjacency() and igraph_weighted_adjacency()).