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

[Gabor Grothendieck]

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 at 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 at utk.edu
> Phone   : Official  - 865 - 974 - 2739 (Aconda Court)
>          Residence - 865 - 946 - 5155
> Webpage : http://web.utk.edu/~rramacha
>
>
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>
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>
>
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