[R] specifying values in correlation matrix in nlme

From: Keyan Zhao <kzhao_at_usc.edu>
Date: Fri 27 May 2005 - 09:16:43 EST


Could anyone help with a linear mixed model fitting problem ?

The model is :

Y= Xp + Zu + e
where X, Z are known design matrix, p is fixed effect factor, u is random effect, u~ (0, G) , e~(0,R)

The main problem is , I want to fix the covariance matrix G to be a constant times a known covariance matrix A, G = c*A (c is positive constant, A is a predefined matrix with values manually set by me.

I know the correlation option in lme function can specify some kind of correlation. but only with the Construct function defined, not whatever ever form I want.

Any good ideas of how to do this in R ?

Thanks a lot in advance,

Keyan Zhao
Computational Biology and Bioinformatics program Univ of Southern California
Email: kzhao@usc.edu



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