R version 2.8.1 (2008-12-22)
Copyright (C) 2008 The R Foundation for Statistical Computing
ISBN 3-900051-07-0

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> x <- runif(10)
> y <- 1+x+rnorm(10,sd=0.1)
> 
> library(bbmle)
> m1 = mle2(y~dnorm(a+b*x,sd=exp(s)),start=list(a=1,b=1,s=log(0.1)))
> 
> m2 = mle2(y~dnorm(a+b*x,sd=exp(s)),start=list(a=1,b=1,s=log(0.1)),
+   method="L-BFGS-B",lower=c(a=0,b=0,s=-Inf))
> 
> m2F = mle2(y~dnorm(a+b*x,sd=exp(s)),start=list(a=1,b=1,s=log(0.1)),
+   method="L-BFGS-B",lower=c(a=0,b=0,s=-Inf),
+   fixed=list(a=1))
Warning message:
In mle2(y ~ dnorm(a + b * x, sd = exp(s)), start = list(a = 1, b = 1,  :
  length mismatch between lower/upper and number of non-fixed parameters
> 
> 
> proc.time()
   user  system elapsed 
  1.008   0.024   1.044