[R] Computing 'exp(1e3)*0' correctly....

[Rui Barradas]

Em 02-09-2012 00:10, Jeff Newmiller escreveu:
> I disagree that this answer is "wrong". If you want a mathematically correct answer you are going to have to obtain it by applying intelligence to the algorithm in which this calculation occurred.

Logarithms are the product of intelligence.
And the standard trick to make this sort of computation.

x <- 1e3
exp(x + log(0))  # zero

x <- 1e300
exp(x + log(0))  # zero

Rui Barradas
>   This is not a mailing list about numerical methods in general, so it probably isn't appropriate to pursue that conversation here.
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> Sent from my phone. Please excuse my brevity.
>
> CHEL HEE LEE <gnustats at gmail.com> wrote:
>
>> I have some trouble to deal the value of 'NaN'.  For example,
>>
>>> exp(1e3)
>> [1] Inf
>>> exp(1e3)*0
>> [1] NaN
>>
>> The correct answer should be 0 rather than NaN.  I will very appreciate
>> if anyone can share some technique to get a correct answer.
>>
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> ______________________________________________
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> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.