Dear all, I am using the nlme package and trying to modelate the variance- covariance matrix of random effects. However, I do not understand why do I get this error message: > M4CompSym <- update(M4,random=A~pdCompSymm(~CED)) Error in pdMatrix.pdCompSymm(x) : Cannot extract the matrix from an uninitialized pdMat object Can anyone please help me? How do I update one Model using one of the pre-defined matrixes? Regards, Sara Mouro Sara Maltez Mouro Centro de Ecologia Funcional Departamento de Botânica Universidade de Coimbra sara@gmesintra.com www.uc.pt/ecology/saramaltezmouro [[alternative HTML version deleted]]