Element 'factor' of a model component is a formula composed of several possible terms described below. It is used to derive a (sparse) precision matrix for a set of coefficient, and possibly a matrix representing a set of linear constraints to be imposed on the coefficient vector.
Independent effects corresponding to the levels of factor f
.
First-order random walk.
Second-order random walk.
First-order autoregressive correlation structure among the levels of f
.
Required argument phi
(fixed number for now).
Dummy seasonal with period period
.
CAR spatial correlation.
Argument poly.df
should be an object of class SpatialPolygonsDataFrame
obtained
e.g. from reading in a shape file with readShapeSpatial
from
package maptools. Arguments snap
and queen
are passed to poly2nb
.
If derive.constraints=TRUE
the constraint matrix for an IGMRF model component
is formed by computing the singular vectors of the precision matrix.
A custom precision or incidence matrix associated with factor f can be passed to argument QD
.