Re: [R] over/under flow

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Mon 04 Jul 2005 - 06:58:33 EST

On 7/3/05, William H. Asquith <wasquith@austin.rr.com> wrote:
> I am porting some FORTRAN to R in which an Inf triggers an if(). The
> trigger is infinite on exp(lgamma(OVER)). What is the canonical R
> style of determining OVER when exp(OVER)== Inf? The code structure
> that I am
> porting is best left intact--so I need to query R somehow to the value
> of OVER that causes exp(lgamma(OVER)) to equal Inf.
>
> On my system,
> exp(lgamma(171)) is about first to equal Inf.
>
> I asked similar question a few weeks ago on exp(OVER) and got the
> answer back as log(.Machine$double.xmax). I now have the lgamma
> involved. I think that answer is what is OVER such the
>
> .Machine$double.xmax = lgamma(OVER),
>
> but I am not sure how to invert or solve for OVER
>

You could just test the result, e.g.

   result <- exp(lgamma(x))
   if (is.finite(result)) ...



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