R Under development (unstable) (2023-12-07 r85661 ucrt) -- "Unsuffered Consequences"
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Platform: x86_64-w64-mingw32/x64

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> require(bbmle)
Loading required package: bbmle
Loading required package: stats4
> mle2a <- function(...)
+   mle2(...)
> 
> mle2b <- function(...)
+   mle2a(...)
> 
> ## some data
> d <- data.frame(x=0:10,y=c(26, 17, 13, 12, 20, 5, 9, 8, 5, 4, 8))
> ym <- mean(d$y)
> 
> ## some fits
> 
> (fit0 <- mle2(y~dpois(lambda=ymean),start=list(ymean=ym),data=d)) # okay

Call:
mle2(minuslogl = y ~ dpois(lambda = ymean), start = list(ymean = ym), 
    data = d)

Coefficients:
   ymean 
11.54545 

Log-likelihood: -42.73 
> predict(fit0)
[1] 11.54545
> (fit0.2 <- mle2(y~dpois(lambda=ymean),start=list(ymean=ym),data=d,
+                 control=list(parscale=2))) # okay

Call:
mle2(minuslogl = y ~ dpois(lambda = ymean), start = list(ymean = ym), 
    data = d, control = list(parscale = 2))

Coefficients:
   ymean 
11.54545 

Log-likelihood: -42.73 
> predict(fit0.2)
[1] 11.54545
> (fit1 <- mle2a(y~dpois(lambda=ymean),start=list(ymean=ym),data=d)) # okay

Call:
mle2(minuslogl = ..1, start = ..2, data = ..3)

Coefficients:
   ymean 
11.54545 

Log-likelihood: -42.73 
> (fit1.2 <- mle2a(y~dpois(lambda=ymean),start=list(ymean=ym),data=d,
+                  control=list(parscale=2))) # FAILS

Call:
mle2(minuslogl = ..1, start = ..2, data = ..3, control = ..4)

Coefficients:
   ymean 
11.54545 

Log-likelihood: -42.73 
> (fit1.3 <- mle2b(y~dpois(lambda=ymean),start=list(ymean=ym),data=d,
+                  control=list(parscale=2))) # FAILS

Call:
mle2(minuslogl = ..1, start = ..2, data = ..3, control = ..4)

Coefficients:
   ymean 
11.54545 

Log-likelihood: -42.73 
> 
> ### NOT WORKING:
> if (FALSE) {
+   predict(fit1)
+   predict(fit1.2)
+   predict(fit1.3)
+ }
> 
> proc.time()
   user  system elapsed 
   1.20    0.07    1.26