Re: [R] over/under flow

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Mon 04 Jul 2005 - 06:43:12 EST

"William H. Asquith" <wasquith@austin.rr.com> writes:

> 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),

Not quite... (see below)  

> but I am not sure how to invert or solve for OVER

> uniroot(function(x) lgamma(x)-log(.Machine$double.xmax), c(171,172))
$root
[1] 171.6244

$f.root
[1] -1.462051e-07

$iter
[1] 3

$estim.prec
[1] 6.103516e-05

-- 
   O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)                  FAX: (+45) 35327907

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Received on Mon Jul 04 06:46:00 2005

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