[R] over/under flow

[Peter Dalgaard]

"William H. Asquith" <wasquith at 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             Øster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
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