# Input format of adjacency matrix

How are the graph edges counted when reading sparse graph adjacency matrix --

are the edges (i,j) and (j,i) connecting vertices i and j counted once or twice?

The manual (for rel. 2.1.1) says that the input file must contain a line for each

vertex/node listing the adjacent vertices of the given vertex. If the vertices

#i and #j are connected, does this mean that the (i+1)th line of the input file

must contain j as an adjacent vertex, and (j+1)th line must contain i as an adjacent

vertex? Also, does the total number of edges count both the edges i-j and j-i

(essentially, counts the same edge twice), or does it count i-j/j-i only once?

Another question: if there are vertices without any neighbours (disconnected),

what should the corresponding lines in the input file contain -- an empty line,

or are such disjoint vertices illegal?

## RE: Input format of adjacency matrix

Just after I posted this I noticed that the first question has been

already answered in the thread "Problems with reading a graph".

Still, what about unconnected vertices (i.e., those that don't have

any neighbours)? Are the corresponding lines in the input file

empty?

## RE: yes, an empty line indicates

yes, an empty line indicates that a vertex has no adjacent vertices. However, you should be removing those vertices from the graph in the first place, as they do not make much sense for partitioning purposes.