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.