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

[Douglas Bates]

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,