[R] Maximization problem in the optim function

[R. Michael Weylandt]

What distribution's log-likelihood are you using? If sigma is supposed
to be square-rooted, you may have to put a constraint or use of abs()
might suffice -- though, admittedly I'm not sure what that will do to
convergence behavior -- but it's hard to help without seeing the
function at hand.

Michael

On Wed, Mar 14, 2012 at 6:57 PM, Niroshan <wnnperer at ucalgary.ca> wrote:
> Dear R Users
>
>
> I am maximizing a user defined log likelihood function. It includes variance
> parameter (sigma). I used R function optim with BFGS maximization method.
> However, it stops before the solution saying “sqrt(sigma): NaNs produced”
> Could anybody know a proper transformation for sigma which can be passed in
> the function?  For the correlation parameter I used Fishers’ transformation
> so it didn’t give any problems. I know we can use ‘L-BFGS-B’ method instead
> of ‘BFGS’. However, it produces some non sensible estimates.
>
> Thanks for taking time
>
>
> --
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