[R] over/under flow

Peter Dalgaard p.dalgaard at biostat.ku.dk
Sun Jul 3 22:43:12 CEST 2005

"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))
[1] 171.6244

[1] -1.462051e-07

[1] 3

[1] 6.103516e-05

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

More information about the R-help mailing list