On Sat, 15 Mar 2008, ianfiske wrote:
>
> If you want to find the value of x such that f(x) = 0, then you can minimize
> f^2 or abs(f) using optim. Hope this helps,
For all but the (default) Nelder-Mead method you will be better off with
f^2 or some other differentiable function than abs(f), since e.g. BFGS
gets its superior convergence results only for locally quadratic objective
functions.
>
> Ian
>
>
>
> francogrex wrote:
>>
>> Hello, optim searches for min (or max) of a function, but is it possible
>> to solve for a specific value? I mean, I want to find the value of a and b
>> that give the function value closest to ZERO (and not min or max) in the
>> below. is it possible? thanks
>>
>> test=function(x){
>> a=x[1]
>> b=x[2]
>> if (all(x>0))(((a/(a+b))*(beta(a,b)/(beta(a,b)-beta(a,b+6))))-0.35259)
>> else Inf
>> }
>> optim(c(1,2),test)
>>
>>
>
> --
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>
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--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
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