[R] Rounding error in seq(...)

[Peter Dalgaard]

Nordlund, Dan (DSHS/RDA) wrote:
>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
>> Behalf Of Douglas Bates
>> Sent: Wednesday, September 30, 2009 3:06 PM
>> To: Peter Dalgaard
>> Cc: r help; Duncan Murdoch
>> Subject: Re: [R] Rounding error in seq(...)
>>
>> On Wed, Sep 30, 2009 at 2:32 PM, Peter Dalgaard<p.dalgaard at biostat.ku.dk>
>> wrote:
>>> Martin Batholdy wrote:
>>>> hum,
>>>>
>>>> can you explain that a little more detailed?
>>>> Perhaps I miss the background knowledge - but it seems just absurd to me.
>>>>
>>>> 0.1+0.1+0.1 is 0.3 - there is no rounding involved, is there?
>>>>
>>>> why is
>>>> x <- 0.1 + 0.1 +0.1
>>>> not equal to
>>>> y <- 0.3
>>> Remember that this is in BINARY arithmetic. It's really not any stranger
>>> than the fact that 1/3 + 1/3 != 2/3 in finite accuracy decimal arithmetic
>>> (0.33333 + 0.33333 = 0.66666 != 0.66667).
>> In an earlier thread on this theme I believe that someone quoted Brian
>> Kernighan as saying "10 times 0.1 is hardly ever 1" but I haven't been
>> able to track down the quote.  Can anyone point us to such a quote?
>> It summarizes the situation succinctly,
>>
> 
> The first page of this document references: http://www.stats.ox.ac.uk/~ruth/RCourse/Numerics.pdf
> 
>  ‘The Elements of Programming Style’ by Kernighan and Plauger

Actually, it cites the R FAQ, Q. 7.31 in extenso...

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