alpha.centrality {igraph} R Documentation

## Find Bonacich alpha centrality scores of network positions

### Description

`alpha.centrality` calculates the alpha centrality of some (or all) vertices in a graph.

### Usage

```alpha.centrality(graph, nodes=V(graph), alpha=1, loops=FALSE,
exo=1, tol=1e-7)
```

### Arguments

 `graph` The input graph, can be directed or undirected `nodes` Vertex sequence, the vertices for which the alpha centrality values are returned. (For technical reasons they will be calculated for all vertices first, anyway.) `alpha` Parameter specifying the relative importance of endogenous versus exogenous factors in the determination of centrality. See details below. `loops` Whether to eliminate loop edges from the graph before the calculation. `exo` The exogenous factors, in most cases this is either a constant – the same factor for every node, or a vector giving the factor for every vertex. Note that long vectors will be truncated and short vectors will be replicated. `tol` Tolerance for near-singularities during matrix inversion, see `solve`.

### Details

The alpha centrality measure can be considered as a generalization of eigenvector centerality to directed graphs. It was proposed by Bonacich in 2001 (see reference below).

The alpha centrality of the vertices in a graph is defined as the solution of the following matrix equation:

x=alpha t(A)x+e,

where A is the (not neccessarily symmetric) adjacency matrix of the graph, e is the vector of exogenous sources of status of the vertices and alpha is the relative importance of the endogenous versus exogenous factors.

### Value

A numeric vector contaning the centrality scores for the selected vertices.

### Warning

Singular adjacency matrices cause problems for this algorithm, the routine may fail is certain cases.

### Author(s)

Gabor Csardi csardi@rmki.kfki.hu.

### References

Bonacich, P. and Paulette, L. (2001). ``Eigenvector-like measures of centrality for asymmetric relations'' Social Networks, 23, 191-201.

`evcent` and `bonpow`

### Examples

```# The examples from Bonacich's paper
g.1 <- graph( c(1,3,2,3,3,4,4,5)-1 )
g.2 <- graph( c(2,1,3,1,4,1,5,1)-1 )
g.3 <- graph( c(1,2,2,3,3,4,4,1,5,1)-1 )
alpha.centrality(g.1)
alpha.centrality(g.2)
alpha.centrality(g.3,alpha=0.5)
```

[Package igraph version 0.5 Index]