[igraph] edges "disapear", when creating graph in R

[zbynek . janoska]

Hello, 

I have encountered following problem in R:

I construct graph from a matrix of edges, but resulting graph has fewer edges than there is rows in the matrix.

# edges are stored in a matrix M

> head(M)

     USEK1 USEK2
[1,]   985   866
[2,]   982   866
[3,]  1062  1039
[4,]  1088  1119
[5,]  1061  1088
[6,]  1060  1061

# matrix stores 3244 edges

> dim(M)

[1] 3244    2

# number of vertices

> max(M)+1

[1] 2404

> g <- graph.empty(n=max(M)+1,directed=T)

> g <- add.edges(g,M)

> g

IGRAPH D--- 2404 3242 --

#########

there are two edges missing.

Can anyone explain, what it the source of this behavior, and how can I fix it?

Best Regards,

Zbynek Janoska
Transport Research Centre

Olomouc, Czech Republic

address@hidden