A (giant) 2-d matrix containing covariate values suitable for passing to
the Fortran code that does the estimation for MRA. This matrix has all the
2-d matrices of the model cbind-ed together. It's dimension is NAN x
NS*(number of coefficients). A convenient way to view the matrix is to assign
a 3-d dimension. I.e., if x is the result of a call to this function
and there are NX coefficients in the model,
then dim(x) <- c(NAN,NS,NX) makes a 3-d matrix with NAN rows, NS columns,
and NX pages. View the covariates for a single animal with x[3,,] or similar
statement.
Names of variables in the model are returned as attribute "variables". Whether
the model has an intercept is returned as attribute "intercept".