R Under development (unstable) (2023-12-07 r85661 ucrt) -- "Unsuffered Consequences"
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> library(bbmle)
Loading required package: stats4
> f <- function() {
+   maxit <- 1000
+   d <- data.frame(x=0:10,
+                   y=c(26, 17, 13, 12, 20, 5, 9, 8, 5, 4, 8))
+   mle2(y~dpois(lambda=exp(lymax)/(1+x/exp(lhalf))),
+    start=list(lymax=0,lhalf=0),
+    data=d,
+    control=list(maxit=maxit),
+    parameters=list(lymax~1,lhalf~1))
+ }
> 
> f2 <- function(method="BFGS") {
+     d <- data.frame(x=0:10,
+                     y=c(26, 17, 13, 12, 20, 5, 9, 8, 5, 4, 8))
+     mle2(y~dpois(lambda=exp(lymax)/(1+x/exp(lhalf))),
+          start=list(lymax=0,lhalf=0),
+          data=d,
+          method=method,
+          parameters=list(lymax~1,lhalf~1))
+ }
> 
> m1 <- f()
> p <- profile(m1)
> ## FIXME: check results (need to save in an environment-friendly way!)
> print(head(as.data.frame(p)),digits=3)
        param      z par.vals.lymax par.vals.lhalf focal
lymax.1 lymax -5.469           2.56          27.21  2.56
lymax.2 lymax -3.204           2.67           2.22  2.67
lymax.3 lymax -2.569           2.78           1.96  2.78
lymax.4 lymax -1.931           2.89           1.73  2.89
lymax.5 lymax -1.292           3.00           1.51  3.00
lymax.6 lymax -0.648           3.11           1.31  3.11
> 
> m2 <- f2()
> p2 <- profile(m2)
> print(head(as.data.frame(p2)),digits=3)
        param      z par.vals.lymax par.vals.lhalf focal
lymax.1 lymax -5.469           2.56          27.21  2.56
lymax.2 lymax -3.204           2.67           2.22  2.67
lymax.3 lymax -2.569           2.78           1.96  2.78
lymax.4 lymax -1.931           2.89           1.73  2.89
lymax.5 lymax -1.292           3.00           1.51  3.00
lymax.6 lymax -0.648           3.11           1.31  3.11
> 
> proc.time()
   user  system elapsed 
   1.37    0.14    1.50