[R] Variance for Vector of Constants is Not Zero

[Jari Oksanen]

On 16 Feb 2006, at 23:17, Uwe Ligges wrote:

> Barry Zajdlik wrote:
>
>> Hi All,
>>
>> An annoying but not critical problem I am having is that the variance 
>> of
>> a vector of constants is reported as > 0. I imagine there is a simple
>> workaround for the following but could not find it after having spent 
>> an
>> embarrassing amount of time.
>>
>> In Splus:
>>
>>
>>> x<-rep(0.02,10)
>>> var(x)
>>> 0
>>
>>
>> In R:
>>
>> x<-rep(0.02,10)
>> var(x)
>> 1.337451e-35
>
>
> Which version of R and which OS is this? I get 0 for both Linux and
> Windows with R-2.2.1.
> Anyway, 0.02 is not well representable and hence can be very well the
> cause for such a numerical inaccuracy.
>
>> I assumed the problem had to do with machine precision and suitably
>> modified .Machine$double.eps and .Machine$double.neg.eps which I 
>> thought
>> would fix the problem but without success. Any pointers to a solution
>> would be appreciated!
>
> Changing .Machine$double.eps does not help to calculate more accurate 
> ...
>
> Uwe Ligges
>
>
>> Cheers,
>> Barry Zajdlik
>>
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>
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--
Jari Oksanen, Oulu, Finland