R Under development (unstable) (2023-12-07 r85661 ucrt) -- "Unsuffered Consequences"
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> require(bbmle)
Loading required package: bbmle
Loading required package: stats4
> x <- 0:10
> y <- c(26, 17, 13, 12, 20, 5, 9, 8, 5, 4, 8)
> d <- data.frame(x,y)
> fit <- mle2(y~dpois(lambda=ymax/(1+x/xhalf)), start=list(ymax=25,xhalf=3),data=d)
> fit2 <- mle2(y~dpois(lambda=(x+1)*slope), start=list(slope=1),data=d)
> BIC(fit)
[1] 62.0039
> BIC(fit,fit2)
     df      BIC
fit   2  62.0039
fit2  1 228.2046
> 
> proc.time()
   user  system elapsed 
   1.09    0.17    1.25