[R] Rounding error in seq(...)
David Winsemius
dwinsemius at comcast.net
Thu Oct 1 00:23:05 CEST 2009
On Sep 30, 2009, at 6:05 PM, Douglas Bates wrote:
> 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,
Number 36 according to this example of "way beyond fair-use":
http://cs.boisestate.edu/~amit/teaching/handouts/style.pdf
>
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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