read_graph function is able to read graphs in various
representations from a file, or from a http connection. Currently some
simple formats are supported.read_graph(file, format = c("edgelist", "pajek", "ncol", "lgl", "graphml",
"dimacs", "graphdb", "gml", "dl"), ...)http or ftp connection. It can also be a character string with
the file name or URI.as_edgelist, pajek, graphml, gml, ncol,
lgl, dimacs and graphdb are supported, the default is
read_graph function may have additional arguments depending on
the file format (the format argument). See the details separately for
each file format, below.write_graph