How to specify user-defined matrix Z?

?Hi all,


In genetic studies, we sometimes include the genetic relatedness matrix as a variance component, so we have this following model:
Y~Xbeta+Zb+error,

where beta are the fixed effects, b~N(0,sigma^2*I) are the random effects, error are the random error, Z is the cholesky decomposition of the known genetic relatedness matrix. So how to use lme4 to fit this model if we know X and Z beforehand? I can use the package "nlme" to do it using the code like

lme(y~-1+X, random=list(group=pdIdent(~-1+Z))),
but how to do it using lme4?

(It's my first time to submit a post, and please let me know if I made anything wrong/inproper.)


Thank you.
Zhengyang


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UT Southwestern


Medical Center



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