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[igraph] Igraph commands about directed and undirected graphs

From: Carlos Eduardo
Subject: [igraph] Igraph commands about directed and undirected graphs
Date: Mon, 12 Sep 2011 09:49:33 -0300



Once lots of commands in igraph demand to choose whether network is directed or undirected, I need some help to understand the follow triad situations (attached a simple diagram illustrating):


Situation 1 (all edges directed):






Situation 2 (the two edges in situation 1, between A and B, were simplified to just one edge undirected):

A<=>B (undirected)

B=>C (directed)

C=>A (directed)


I did measures of density, centrality degree, indegree, outdegree, betweenness and closeness.


The difference was noticed only in centrality degree (situation 1: A and B have 3 / situation 2: A and B have 2). So, in situation 2, I have valued the undirected edge to 2 and the others (directed) to 1. After that, using edge strength in centrality degree measure, the result was equal to both situations.


a) Is the simplification illustrated in situation 2 correct (two directed edges between A and B simplified to one undirected edge)?


b) Is there any problem about building networks as illustrated in situation 2 (directed and undirected edges handled/represented together)?


c) Is the procedure about edge value correct (to obtain the same centrality degree in both situations)? Is it really necessary?


d) Could I point in igraph commands situation 2 (with undirected and directed edges together) as a directed graph?


Thanks indeed in advance,


Attachment: Directed and undirected graphs.png
Description: PNG image

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