Re: [R] R- exp(-1000) ? - how to get R to give me an actual answer ?

From: Gabor Grothendieck <ggrothendieck_at_gmail.com>
Date: Wed 26 Oct 2005 - 15:42:14 EST

Since log base 10 is log(x)/log(10) the exponent is:

	floor(log(exp(-1000))/log(10))
	= floor(-1000/log(10))

which in an R session gives:

	> floor(-1000/log(10))
	[1] -435

and the mantissa is:

	exp(-1000)/10^(-435)
	= exp(-1000)/exp(-435*log(10))
	= exp(-1000+435*log(10))

which in an R session gives:

	> exp(-1000+435*log(10))
	[1] 5.075959

Thus the answer is 5.075959e-435 though, of course, we can't represent that directly on your computer.

We can double check this with yacas which is a free computer algebra system that supports arbitrary precision math:

   In> N(Exp(-1000))
   Out> 0.5075958898e-434

On 10/26/05, rramacha <rramacha@utk.edu> wrote:
> Dear All,
>
> I am a novice user of the R software package. When I try and compute,
> exp(-1000) or exp(-2000), i get the answer as zero. Is there any way i can get
> R to compute the answer and give me an actual number ? ( by increasing the
> precision or any other method).
>
> If I cannot get R to give me a number, can anybody give me some advice on how
> to manually compute this number ?
>
> I would greatly appreciate your help on this issue.
>
> Thanks
> Ravi
>
> Ravichandran "Ravi" Ramachandran
>
> Graduate Teaching Assistant
> Department of Statistics
> The University of Tennessee,Knoxville
> USA
> E-mail : ravi@utk.edu
> Phone : Official - 865 - 974 - 2739 (Aconda Court)
> Residence - 865 - 946 - 5155
> Webpage : http://web.utk.edu/~rramacha
>
>
> " Space maybe the final frontier
> But its made in a Hollywood basement
> - The Red Hot Chilli Peppers - 'Californication'
>
> Space maybe the final frontier
> But it can be 'replicated' in a Hollywood basement
> - Me, after taking the Stat 573 class
> "
>
>
> "Thank God every day when you get up that you have something to do that day which must be done whether you like it or not. Being forced to work and forced to do your best will breed in you temperance and self-control, diligence and strength of will"
> - Basil Carpenter
>
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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 Wed Oct 26 15:47:45 2005

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