createAdj function

Creates an Adjacency Matrix

Creates an adjacency matrix in a form suitable for using in BRugs or WinBUGS.

createAdj(matrix, filename = "Adj.txt", suffix = NULL)

Arguments

• matrix: square matrix with 1's for neighbours and NA's for non-neighbours.
• filename: filename that the adjacency matrix file will be written to (default=Adj.txt ).
• suffix: string to be appended to num , adj and weights object names

Returns

Creates a text file named filename that contains the total number of neighbours (num), the index number of the adjacent neighbours (adj) and the weights (weights).

Details

Adjacency matrices are used by conditional autoregressive (CAR) models to smooth estimates according to some neighbourhood map. The basic idea is that neighbouring areas have more in common than non-neighbouring areas and so will be positively correlated.

As well as correlations in space it is possible to use CAR models to model similarities in time.

In this case the matrix represents those time points that we wish to assume to be correlated.

Examples

# Nearest neighbour matrix for 5 time points
x = c(NA,1,NA,NA,NA)
(V = toeplitz(x))
createAdj(V)

Author(s)

Adrian Barnett a.barnett@qut.edu.au