precmat is a wrapper that calls the other functions
according to the argument type.
Implements many of the precision matrices discussed in Chapter
3 of Rue and Held (2005). For example, precmat.RW1,
precmat.RW2 and precmat.season are given in
equations (3.22), (3.40) and (3.59); precmat.IGMRFreglat on
page 107. Note that for the latter we reverse the order of the dimension here!
If adjacency matrix is a regular matrix, it is coerced to a
spam object. Only the structure is used. Make sure, that the
diagonal is empty.
# NOT RUN {n <- 10
Q <- precmat.RW2( n)
# rmvnorm.prec(1, Q=Q) # does not work, because the matrix is singular.
Q
# }# NOT RUN {<!-- %*%cbind(1,1:n) -->
# }