Re: [Rd] bug? (PR#8074)

From: Paul Mosquin <pmosquin_at_hotmail.com>
Date: Wed 17 Aug 2005 - 01:33:13 GMT


Thomas,

Thank you for your response. I checked the FAQ and it provides an example using sqrt(2) where you'd expect numerical precision to be an issue.

I guess that I expect R to act pretty much as C or C++ would do if I were to program the same code. It's a bit of a surprise that assignment of rationals, well within precision, followed by multiplication leading to a result well within precision picks up those extra bits along the way. Something to watch out for, to be sure.

Thanks again for your help

Paul

>From: Thomas Lumley <tlumley@u.washington.edu>
>To: pmosquin@hotmail.com
>CC: r-devel@stat.math.ethz.ch, R-bugs@biostat.ku.dk
>Subject: Re: [Rd] bug? (PR#8074)
>Date: Tue, 16 Aug 2005 16:06:48 -0700 (PDT)
>
>On Wed, 17 Aug 2005 pmosquin@hotmail.com wrote:
>>I just don't understand this:
>>
>>>(2*2)==4
>>[1] TRUE
>>>.2*.2
>>[1] 0.04
>>>(.2*.2)==.04
>>[1] FALSE
>
>It's a FAQ, not a bug. Consider:
>
>>(.2*.2) - .04
>[1] 6.938894e-18
>
>and read the FAQ
>
> -thomas
>
>
>>or
>>
>>>x=.04
>>>x
>>[1] 0.04
>>>y=.2*.2
>>>y
>>[1] 0.04
>>>y==x
>>[1] FALSE
>>
>>______________________________________________
>>R-devel@r-project.org mailing list
>>https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
>Thomas Lumley Assoc. Professor, Biostatistics
>tlumley@u.washington.edu University of Washington, Seattle



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https://stat.ethz.ch/mailman/listinfo/r-devel Received on Wed Aug 17 11:36:13 2005

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