Nordlund, Dan (DSHS/RDA) wrote:
-----Original Message-----
From: r-help-boun...@r-project.org [mailto:r-help-boun...@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.dalga...@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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