R version 4.4.0 beta (2024-04-14 r86421 ucrt) -- "Puppy Cup"
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Platform: x86_64-w64-mingw32/x64

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> if (lme4:::testLevel() > 1 || .Platform$OS.type != "windows") withAutoprint({
+ 
+     ## testing whether lme4 and nlme play nicely.  Only known issue
+     ## is lmList-masking ...
+     library("lme4")
+     library("nlme")
+     fm1_lmer <- lmer(Reaction ~ Days   +       (Days|Subject), sleepstudy)
+     fm1_lme  <- lme (Reaction ~ Days, random = ~Days|Subject,  sleepstudy)
+     ## variance-covariance matrices: annoyingly different structures
+     vc_lmer <- VarCorr(fm1_lmer)
+     vc_lme  <- VarCorr(fm1_lme, rdig = 8)
+     suppressWarnings(storage.mode(vc_lme) <- "numeric")# 2 NAs
+     vc_lmerx <- c(diag(vc_lmer[[1]]), attr(vc_lmer[[1]],"correlation")[1,2])
+     vc_lmex  <- c( vc_lme[1:2,1],     vc_lme[2,3])
+     stopifnot(
+         all.equal(vc_lmex, vc_lmerx, tolerance= 4e-4) # had 3e-5, now see 0.000296
+       , ## fixed effects (much easier) :
+         all.equal(fixef(fm1_lmer), fixef(fm1_lme)) # 3.6e-15
+        ,
+         all.equal(unname(unlist(unclass(ranef(fm1_lmer)))),
+                   unname(unlist(unclass(ranef(fm1_lme)))),
+                   tolerance = 2e-4) # had 2e-5, now see 8.41e-5
+     )
+ 
+     fm1L_lme  <- nlme::lmList(distance ~ age | Subject, Orthodont)
+     fm1L_lmer <- lme4::lmList(distance ~ age | Subject, Orthodont)
+     stopifnot(all.equal(fixef(fm1L_lmer),
+                         fixef(fm1L_lme)))
+     sm1L_e  <- summary(fm1L_lme)
+     sm1L_er <- summary(fm1L_lmer)
+     stopifnot(
+         all.equal(coef(sm1L_e),
+                   coef(sm1L_er), tol=1e-12)# even tol=0 works on some Lnx 64b
+     )
+ 
+     ## FIXME: test opposite order
+ })
> 
> proc.time()
   user  system elapsed 
   1.06    0.10    1.10