In the documnt, http://igraph.sourceforge.net/doc/R/read.graph.html
NCOL format
This format is used by the Large Graph Layout program (http://bioinformatics.icmb.utexas.edu/lgl), and it is simply a symbolic weighted edge list. It is a simple text file with one edge per line. An edge is defined by two symbolic vertex names separated by whitespace. (The symbolic vertex names themselves cannot contain whitespace.) They might followed by an optional number, this will be the weight of the edge; the number can be negative and can be in scientific notation. If there is no weight specified to an edge it is assumed to be zero.
The resulting graph is always undirected. LGL cannot deal with files which contain multiple or loop edges, this is however not checked here, as igraph is happy with these.
What does the sentence (The resulting graph is always undirected.) mean?
I read the data using the ncol format.
g<-read.graph("file.ncol",format="ncol",directed=TRUE)
is.directed(g)
TRUE
The result is TRUE. So I think the graph is directed. But why the document says the resulting graph is always undirected?
