From: William H. Asquith <wasquith_at_austin.rr.com>

Date: Mon 04 Jul 2005 - 07:00:40 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Mon Jul 04 07:04:30 2005

Date: Mon 04 Jul 2005 - 07:00:40 EST

Great, but to followup, how do I select the bounds (B,E) on the root for an arbitrary machine?

OVER = uniroot(function(x) lgamma(x)-log(.Machine$double.xmax), c(B,E))$root

If uniroot() is fast enough, is it appropriate for me to set B at say 1 and E at log(.Machine$double.max)? Suggestions on do this the proper "R way"? Perhaps this . . .

OVER = uniroot(function(x) lgamma(x)-log(.Machine$double.xmax), c(1,log(.Machine$double.xmax)))$root

I am working on a package so different machines will be involved thus simple 171,172 might not be the best idea for the root?

**THANKS!
**
-wha

On Jul 3, 2005, at 3:43 PM, Peter Dalgaard wrote:

> "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
**>
*

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Mon Jul 04 07:04:30 2005

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