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Evaluating Z matrix
3 messages · Pantelis Hadjipantelis, Ben Bolker
1 day later
Pantelis Hadjipantelis <kalakouentin at ...> writes:
Hello, I am going through lme4's book chapters and among the things that are slightly in disparity with the current state of things is the structure of Zt. Namely in chapter 3, section 2, Fig 3.4 presents the images of the Z^T matrices for the models: (fm06 <- lmer(Reaction ~ 1 + Days + (1 + Days|Subject), sleepstudy, REML=FALSE)); image(fm06 <at> Zt) (fm07 <- lmer(Reaction ~ 1 + Days + (1|Subject) + (0+Days|Subject), sleepstudy, REML=FALSE)); image(fm07 <at> Zt) and while in the book they appear different now they appear the same. I understand that the "important bit" is the L matrix that does remain "unchanged" but getting a different Z matrix than before does seem odd. What is the reason of this change in the generation of Z and ?? from the random-effects terms?
There have been several major changes in the internal structures of the lme4 package in the last couple of years. The structure of Z has simply changed as a side effect. In fact, the development version of lme4 has reverted to a behaviour more like the version from 2010, where (x|grp) and (1|grp)+(0+x|grp) give differently structured Z matrices.
If lme4 book is not the most update to date reference about the generation of Z in lme4, what resource is?
Unfortunately, the code -- specifically the lme4:::mkReTrms function. But you should feel free to keep asking questions here.
Just to clarifty I am using: MEMSS_0.9-0, lme4_0.999999-0, Matrix_1.0-11. lme4's book version is that of June 25, 2010. Thank you in advance. All best, Pantelis Hadjipantelis
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