Creates an Adjacency Matrix

Creates an adjacency matrix in a form suitable for use with nimble

Usage

createAdj(matrix, suffix = NULL)

Arguments

matrix

square matrix with 1's for neighbours and NA's for non-neighbours.

suffix

string to be appended to "num", "adj" and "weights" object names

Value

A list of:

• num: the total number of neighbours

• adj: the index number of the adjacent neighbours

• 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.

Author

Adrian Barnett a.barnett@qut.edu.au

Examples

# \donttest{
# Nearest neighbour matrix for 5 time points
x <- c(NA,1,NA,NA,NA)
V <- toeplitz(x)
V
#>      [,1] [,2] [,3] [,4] [,5]
#> [1,]   NA    1   NA   NA   NA
#> [2,]    1   NA    1   NA   NA
#> [3,]   NA    1   NA    1   NA
#> [4,]   NA   NA    1   NA    1
#> [5,]   NA   NA   NA    1   NA
createAdj(V)
#> $num
#> [1] 1 2 2 2 1
#> 
#> $adj
#> [1] 2 1 3 2 4 3 5 4
#> 
#> $weight
#> [1] 1 1 1 1 1 1 1 1
#> 
# }