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@Zt)
(fm07 <- lmer(Reaction ~ 1 + Days + (1|Subject) + (0+Days|Subject),
sleepstudy, REML=FALSE)); image(fm07@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 Λ from the
random-effects terms?
If lme4 book is not the most update to date reference about the generation
of Z in lme4, what resource is?

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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