R Under development (unstable) (2023-12-07 r85661 ucrt) -- "Unsuffered Consequences"
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> ## try to reconstruct error reported by Hofert Jan Marius
> ## (simpler version)
> 
> Lfun <- function(x) {
+   (x-5)^2
+ }
> 
> 
> 
> library(bbmle)
Loading required package: stats4
> 
> lb <- 6
> ## first try with L-BFGS-B and bounds
> m1 <- mle2(Lfun,start=list(x=7),lower=6,method="L-BFGS-B")
Warning message:
In mle2(Lfun, start = list(x = 7), lower = 6, method = "L-BFGS-B") :
  some parameters are on the boundary: variance-covariance calculations based on Hessian may be unreliable
> coef(m1)
x 
6 
> p1 <- profile(m1)
> plot(p1)
> (c1 <- confint(m1,quietly=TRUE))
   2.5 %   97.5 % 
      NA 6.702747 
> ## all  OK
> 
> m2 <- mle2(Lfun,start=list(x=7),optimizer="optimize",
+            lower=lb,upper=10)
> coef(m2)
      x 
6.00006 
> p2 <- profile(m2)
> (c2 <- confint(m2))
   2.5 %   97.5 % 
      NA 6.668954 
> (c2 <- confint(m2))
   2.5 %   97.5 % 
      NA 6.668954 
> plot(p2,show.points=TRUE)
Warning messages:
1: In .local(x, ...) :
  non-monotonic profile: reverting to linear interpolation.  Consider setting std.err manually
2: In regularize.values(x, y, ties, missing(ties), na.rm = na.rm) :
  collapsing to unique 'x' values
> 
> proc.time()
   user  system elapsed 
   1.70    0.15    1.86