R Under development (unstable) (2012-07-27 r60013) -- "Unsuffered Consequences"
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ISBN 3-900051-07-0
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> ## from Eric Weese
> library(bbmle)
> f <- function(x=2,a=1) x^2 - a
> f.g <- function(x,a) 2*x
> f.g2 <- function(x,a) c(2*x,0)
> mle2(f,fixed=list(a=1))

Call:
mle2(minuslogl = f, fixed = list(a = 1))

Coefficients:
           x            a 
1.092459e-13 1.000000e+00 

Log-likelihood: 1 
> mle2(f,gr=f.g,fixed=list(a=1))

Call:
mle2(minuslogl = f, fixed = list(a = 1), gr = f.g)

Coefficients:
x a 
0 1 

Log-likelihood: 1 
> mle2(f,gr=f.g2,fixed=list(a=1))

Call:
mle2(minuslogl = f, fixed = list(a = 1), gr = f.g2)

Coefficients:
x a 
0 1 

Log-likelihood: 1 
> 
> proc.time()
   user  system elapsed 
  0.736   1.088   1.652