First and second order adjacency structure of the counties
in the contiguous United States. We consider that two counties
are neighbors if they share at
least one edge of their polygon description in maps
.
Two matrices of class spam
- UScounties.storder
Contains a one in the i
and j
element if county
i
is a neighbor of county j
.
- UScounties.ndorder
Contains a one in the i
and j
element if counties
i
and j
are a neighbors of county k
and counties
i
and j
are not neighbors.
Examples
# number of counties:
n <- nrow( UScounties.storder)
if (FALSE) { # \dontrun{
# make a precision matrix
Q <- diag.spam( n) + .2 * UScounties.storder + .1 * UScounties.ndorder
display( as.spam( chol( Q)))
} # }