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#' Get the number of automorphisms
#'
#' @description
#'
#' Get the number of automorphisms the graph contains. An automorphism of a
#' graph is a form of symmetry in which the graph is mapped onto itself while
#' preserving edge-node connectivity.
#'
#' @inheritParams render_graph
#'
#' @return A single numeric value representing the number of automorphisms the
#' graph contains.
#'
#' @examples
#' # Create a cycle graph
#' graph <-
#' create_graph() %>%
#' add_cycle(n = 5)
#'
#' # Get a count of automorphisms
#' graph %>%
#' count_automorphisms()
#'
#' # Create a full graph and then
#' # count the automorphisms
#' create_graph() %>%
#' add_full_graph(n = 10) %>%
#' count_automorphisms()
#'
#' @export
count_automorphisms <- function(graph) {
# Get the name of the function
fcn_name <- get_calling_fcn()
# Validation: Graph object is valid
if (graph_object_valid(graph) == FALSE) {
emit_error(
fcn_name = fcn_name,
reasons = "The graph object is not valid")
}
# If the graph is empty, then return NA
if (nrow(graph$nodes_df) == 0) {
return(as.numeric(NA))
}
# Convert the graph to an undirected graph
graph_undirected <- set_graph_undirected(graph)
# Convert the graph to an igraph object
ig_graph <- to_igraph(graph_undirected)
# Get the number of automorphisms in
# the graph
igraph::automorphisms(
graph = ig_graph,
sh = "fm")["group_size"] %>%
unlist() %>%
as.numeric()
}
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