feat: is_clique() and is_ivs() test whether a set of vertices for…

…ms a clique or an independent set

NAMESPACE

@@ -548,6 +548,7 @@ export(is_acyclic)
 export(is_biconnected)
 export(is_bipartite)
 export(is_chordal)
+export(is_clique)
 export(is_complete)
 export(is_connected)
 export(is_dag)
@@ -558,6 +559,7 @@ export(is_graphical)
 export(is_hierarchical)
 export(is_igraph)
 export(is_isomorphic_to)
+export(is_ivs)
 export(is_matching)
 export(is_max_matching)
 export(is_min_separator)

R/cliques.R

@@ -164,6 +164,8 @@ clique.number <- function(graph) { # nocov start
 #' `clique_size_counts()` returns a numeric vector representing a histogram
 #' of clique sizes, between the given minimum and maximum clique size.
 #'
+#' `is_clique()` tests whether all pairs within a vertex set are connected.
+#'
 #' @inheritParams weighted_cliques
 #' @param graph The input graph, directed graphs will be considered as
 #'   undirected ones, multiple edges and loops are ignored.
@@ -205,6 +207,9 @@ clique.number <- function(graph) { # nocov start
 #' # To have a bit less maximal cliques, about 100-200 usually
 #' g <- sample_gnp(100, 0.03)
 #' max_cliques(g)
+#'
+#' # Check that all returned vertex sets are indeed cliques
+#' all(sapply(max_cliques(g), function (c) is_clique(g, c)))
 #' @cdocs igraph_cliques
 cliques <- cliques_impl
 
@@ -395,6 +400,8 @@ weighted_clique_num <- weighted_clique_number_impl
 #' These functions use the algorithm described by Tsukiyama et al., see
 #' reference below.
 #'
+#' `is_ivs()` tests if no pairs within a vertex set are connected.
+#'
 #' @param graph The input graph, directed graphs are considered as undirected,
 #'   loop edges and multiple edges are ignored.
 #' @param min Numeric constant, limit for the minimum size of the independent
@@ -550,3 +557,30 @@ clique_size_counts <- function(graph, min = 0, max = 0, maximal = FALSE) {
 #' g <- as_undirected(g)
 #' is_complete(g)
 is_complete <- is_complete_impl
+
+#' @rdname cliques
+#'
+#' @description
+#' Tests if all pairs within a set of vertices are adjacent, i.e. whether they
+#' form a clique. An empty set and singleton set are considered to be a clique.
+#'
+#' @param graph The input graph.
+#' @param candidate The vertex set to test for being a clique.
+#' @param directed Whether to consider edge directions.
+#' @return `is_clique()` returns `TRUE` if the candidate vertex set forms
+#'   a clique.
+#' @keywords graphs
+#' @export
+#' @cdocs igraph_is_clique
+is_clique <- is_clique_impl
+
+#' @rdname ivs
+#'
+#' @param graph The input graph.
+#' @param candidate The vertex set to test for being an independent set.
+#' @return `is_ivs()` returns `TRUE` if the candidate vertex set forms an
+#'   independent set.
+#' @keywords graphs
+#' @export
+#' @cdocs igraph_is_independent_vertex_set
+is_ivs <- is_independent_vertex_set_impl