Add graph references
This commit is contained in:
Abdelrahman Said
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/*
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igraph library.
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Copyright (C) 2024 The igraph development team <igraph@igraph.org>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <https://www.gnu.org/licenses/>.
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*/
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#include "igraph_reachability.h"
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#include "igraph_adjlist.h"
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#include "igraph_bitset_list.h"
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#include "igraph_components.h"
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#include "igraph_constructors.h"
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#include "igraph_interface.h"
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/**
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* \ingroup structural
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* \function igraph_reachability
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* \brief Calculates which vertices are reachable from each vertex in the graph.
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*
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* The resulting list will contain one bitset for each strongly connected component.
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* The bitset for component i will have its j-th bit set, if vertex j is reachable
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* from some vertex in component i in 0 or more steps.
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* In particular, a vertex is always reachable from itself.
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*
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* \param graph The graph object to analyze.
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* \param membership Pointer to an integer vector. For every vertex,
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* the ID of its component is given. The vector will be resized as needed.
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* This parameter must not be \c NULL.
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* \param csize Pointer to an integer vector or \c NULL. For every component, it
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* gives its size (vertex count), the order being defined by the component
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* IDs. The vector will be resized as needed.
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* \param no_of_components Pointer to an integer or \c NULL. The number of
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* components will be stored here.
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* \param reach A list of bitsets representing the result. It will be resized
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* as needed. <code>reach[membership[u]][v]</code> is set to \c true if
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* vertex \c v is reachable from vertex \c u.
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* \param mode In directed graphs, controls the treatment of edge directions.
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* Ignored in undirected graphs. With \c IGRAPH_OUT, reachability is computed
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* by traversing edges along their direction. With \c IGRAPH_IN, edges are
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* traversed opposite to their direction. With \c IGRAPH_ALL, edge directions
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* are ignored and the graph is treated as undirected.
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* \return Error code:
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* \c IGRAPH_ENOMEM if there is not enough memory
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* to perform the operation.
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*
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* \sa \ref igraph_connected_components() to find the connnected components
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* of a graph; \ref igraph_count_reachable() to count how many vertices
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* are reachable from each vertex; \ref igraph_subcomponent() to find
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* which vertices are rechable from a single vertex.
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*
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* Time complexity: O(|C||V|/w + |V| + |E|), where
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* |C| is the number of strongly connected components (at most |V|),
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* |V| is the number of vertices, and
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* |E| is the number of edges respectively,
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* and w is the bit width of \type igraph_int_t, typically the
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* word size of the machine (32 or 64).
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*/
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igraph_error_t igraph_reachability(
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const igraph_t *graph,
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igraph_vector_int_t *membership,
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igraph_vector_int_t *csize,
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igraph_int_t *no_of_components,
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igraph_bitset_list_t *reach,
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igraph_neimode_t mode) {
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const igraph_int_t no_of_nodes = igraph_vcount(graph);
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igraph_int_t no_of_comps;
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igraph_adjlist_t adjlist, dag;
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if (mode != IGRAPH_ALL && mode != IGRAPH_OUT && mode != IGRAPH_IN) {
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IGRAPH_ERROR("Invalid mode for reachability.", IGRAPH_EINVMODE);
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}
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if (! igraph_is_directed(graph)) {
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mode = IGRAPH_ALL;
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}
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IGRAPH_CHECK(igraph_connected_components(graph,
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membership, csize, &no_of_comps,
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mode == IGRAPH_ALL ? IGRAPH_WEAK : IGRAPH_STRONG));
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if (no_of_components) {
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*no_of_components = no_of_comps;
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}
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IGRAPH_CHECK(igraph_bitset_list_resize(reach, no_of_comps));
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for (igraph_int_t comp = 0; comp < no_of_comps; comp++) {
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IGRAPH_CHECK(igraph_bitset_resize(igraph_bitset_list_get_ptr(reach, comp), no_of_nodes));
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}
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for (igraph_int_t v = 0; v < no_of_nodes; v++) {
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IGRAPH_BIT_SET(*igraph_bitset_list_get_ptr(reach, VECTOR(*membership)[v]), v);
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}
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if (mode == IGRAPH_ALL) {
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return IGRAPH_SUCCESS;
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}
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IGRAPH_CHECK(igraph_adjlist_init(graph, &adjlist, mode, IGRAPH_LOOPS_ONCE, IGRAPH_MULTIPLE));
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IGRAPH_FINALLY(igraph_adjlist_destroy, &adjlist);
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IGRAPH_CHECK(igraph_adjlist_init_empty(&dag, no_of_comps));
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IGRAPH_FINALLY(igraph_adjlist_destroy, &dag);
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for (igraph_int_t v = 0; v < no_of_nodes; v++) {
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const igraph_vector_int_t *neighbours = igraph_adjlist_get(&adjlist, v);
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igraph_vector_int_t *dag_neighbours = igraph_adjlist_get(&dag, VECTOR(*membership)[v]);
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const igraph_int_t n = igraph_vector_int_size(neighbours);
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for (igraph_int_t i = 0; i < n; i++) {
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igraph_int_t w = VECTOR(*neighbours)[i];
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if (VECTOR(*membership)[v] != VECTOR(*membership)[w]) {
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IGRAPH_CHECK(igraph_vector_int_push_back(dag_neighbours, VECTOR(*membership)[w]));
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}
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}
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}
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/* Iterate through strongly connected components in reverser topological order,
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* exploiting the fact that they are indexed in topological order. */
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for (igraph_int_t i = 0; i < no_of_comps; i++) {
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const igraph_int_t comp = mode == IGRAPH_IN ? i : no_of_comps - i - 1;
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const igraph_vector_int_t *dag_neighbours = igraph_adjlist_get(&dag, comp);
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igraph_bitset_t *from_bitset = igraph_bitset_list_get_ptr(reach, comp);
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const igraph_int_t n = igraph_vector_int_size(dag_neighbours);
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for (igraph_int_t j = 0; j < n; j++) {
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const igraph_bitset_t *to_bitset = igraph_bitset_list_get_ptr(reach, VECTOR(*dag_neighbours)[j]);
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igraph_bitset_or(from_bitset, from_bitset, to_bitset);
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}
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}
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igraph_adjlist_destroy(&adjlist);
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igraph_adjlist_destroy(&dag);
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IGRAPH_FINALLY_CLEAN(2);
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return IGRAPH_SUCCESS;
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}
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/**
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* \ingroup structural
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* \function igraph_count_reachable
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* \brief The number of vertices reachable from each vertex in the graph.
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*
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* \param graph The graph object to analyze.
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* \param counts Integer vector. <code>counts[v]</code> will store the number
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* of vertices reachable from vertex \c v, including \c v itself.
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* \param mode In directed graphs, controls the treatment of edge directions.
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* Ignored in undirected graphs. With \c IGRAPH_OUT, reachability is computed
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* by traversing edges along their direction. With \c IGRAPH_IN, edges are
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* traversed opposite to their direction. With \c IGRAPH_ALL, edge directions
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* are ignored and the graph is treated as undirected.
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* \return Error code:
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* \c IGRAPH_ENOMEM if there is not enough memory
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* to perform the operation.
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*
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* \sa \ref igraph_connected_components(), \ref igraph_transitive_closure()
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*
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* Time complexity: O(|C||V|/w + |V| + |E|), where
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* |C| is the number of strongly connected components (at most |V|),
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* |V| is the number of vertices, and
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* |E| is the number of edges respectively,
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* and w is the bit width of \type igraph_int_t, typically the
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* word size of the machine (32 or 64).
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*/
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igraph_error_t igraph_count_reachable(const igraph_t *graph,
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igraph_vector_int_t *counts,
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igraph_neimode_t mode) {
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igraph_vector_int_t membership;
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igraph_int_t no_of_nodes = igraph_vcount(graph);
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igraph_bitset_list_t reach;
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IGRAPH_VECTOR_INT_INIT_FINALLY(&membership, 0);
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IGRAPH_BITSET_LIST_INIT_FINALLY(&reach, 0);
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IGRAPH_CHECK(igraph_reachability(graph, &membership, NULL, NULL, &reach, mode));
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IGRAPH_CHECK(igraph_vector_int_resize(counts, igraph_vcount(graph)));
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for (igraph_int_t i = 0; i < no_of_nodes; i++) {
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VECTOR(*counts)[i] = igraph_bitset_popcount(igraph_bitset_list_get_ptr(&reach, VECTOR(membership)[i]));
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}
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igraph_bitset_list_destroy(&reach);
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igraph_vector_int_destroy(&membership);
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IGRAPH_FINALLY_CLEAN(2);
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return IGRAPH_SUCCESS;
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}
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/**
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* \ingroup structural
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* \function igraph_transitive_closure
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* \brief Computes the transitive closure of a graph.
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*
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* The resulting graph will have an edge from vertex \c i to vertex \c j
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* if \c j is reachable from \c i.
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*
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* \param graph The graph object to analyze.
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* \param closure The resulting graph representing the transitive closure.
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* \return Error code:
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* \c IGRAPH_ENOMEM if there is not enough memory
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* to perform the operation.
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*
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* \sa \ref igraph_connected_components(), \ref igraph_count_reachable()
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*
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* Time complexity: O(|V|^2 + |E|), where
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* |V| is the number of vertices, and
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* |E| is the number of edges, respectively.
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*/
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igraph_error_t igraph_transitive_closure(const igraph_t *graph, igraph_t *closure) {
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const igraph_int_t no_of_nodes = igraph_vcount(graph);
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const igraph_bool_t directed = igraph_is_directed(graph);
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igraph_vector_int_t membership, edges;
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igraph_bitset_list_t reach;
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IGRAPH_VECTOR_INT_INIT_FINALLY(&membership, 0);
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IGRAPH_BITSET_LIST_INIT_FINALLY(&reach, 0);
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IGRAPH_CHECK(igraph_reachability(graph, &membership, NULL, NULL, &reach, IGRAPH_OUT));
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IGRAPH_VECTOR_INT_INIT_FINALLY(&edges, 0);
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for (igraph_int_t u = 0; u < no_of_nodes; u++) {
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const igraph_bitset_t *row = igraph_bitset_list_get_ptr(&reach, VECTOR(membership)[u]);
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for (igraph_int_t v = directed ? 0 : u + 1; v < no_of_nodes; v++) {
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if (u != v && IGRAPH_BIT_TEST(*row, v)) {
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IGRAPH_CHECK(igraph_vector_int_push_back(&edges, u));
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IGRAPH_CHECK(igraph_vector_int_push_back(&edges, v));
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}
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}
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}
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igraph_bitset_list_destroy(&reach);
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igraph_vector_int_destroy(&membership);
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IGRAPH_FINALLY_CLEAN(2);
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IGRAPH_CHECK(igraph_create(closure, &edges, no_of_nodes, directed));
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igraph_vector_int_destroy(&edges);
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IGRAPH_FINALLY_CLEAN(1);
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return IGRAPH_SUCCESS;
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}
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