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I have a network in the form of an adjacency matrix, and I am trying to create a plot that shows the degree distribution of the network.

First of all, I used the function "graph.adjacency" to create an igraph object from the adjacency matrix, and I obtained the connectivity for each node with the "degree" function:

graphobj<-graph.adjacency(adjacencymatrix, mode="undirected")

degreenetwork<-degree(graphobj)

Then I have calculated the degree of each node with an other method:

degreenetwork2<-apply(adjacencymatrix, 1,sum)

and I have noticed that the degree of the nodes is not always preserved. In fact the the two methods give me different value of connectivity for the nodes. For example:

mean(degreenetwork)

[1] 156.068

mean(degreenetwork2)

[1] 78.034

min(degreenetwork)

[1] 17

min(degreenetwork2)

[1] 0

max(degreenetwork)

[1] 521

max(degreenetwork2)

[1] 452

Is there something wrong, or am I not using correctly the igraph package?

Regards

Gianni

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1 Answers1

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You are possibly double counting edges, because your matrix is probably symmetric. Or maybe your matrix is not binary. It is hard to tell for sure, because you did not provide a reproducible example, so we have no idea what is in your matrix.

See How to make a great R reproducible example?.

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Gabor Csardi
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  • I think I have solved the problem, I just got confused, I wanted to calculate the degree of each node considering only the rows of the adjacency matrix. Your package works perfectly. Thank you very much for your answer and time anyway. –  May 13 '14 at 16:09