[R] kronecker product in mixed model

[Suyan Tian]

Hi, does anyone know how to self-define the variance-covariance  
structure of the within-subject variance for the mixed models , i.g,

yi=Xibeta+Zibi+ei

For ei I want to use kronecker product so its variance matrix will be  
R=V*E,  here * represents Kronecker product.

Thanks so many.