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rampaletienne
2019 Feb 20
0
code for sum function
...ed a possibly platform-dependent
higher-than-double-precision type.
By the way, in my example involving rep(1/3, n) I neglected to include the
most precise
way to calculate the sum: n%/%3 + (n%%3)/3.
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Wed, Feb 20, 2019 at 2:45 PM Rampal Etienne <rampaletienne at gmail.com>
wrote:
> Dear Will,
>
> This is exactly what I find.
> My point is thus that the sum function in R is not a naive sum nor a
> Kahansum (in all cases), but what algorithm is it using then?
>
> Cheers, Rampal
>
>
> On Tue, Feb 19, 2019, 19:08 William D...
2019 Feb 19
4
code for sum function
The algorithm does make a differece. You can use Kahan's summation
algorithm (https://en.wikipedia.org/wiki/Kahan_summation_algorithm) to
reduce the error compared to the naive summation algorithm. E.g., in R
code:
naiveSum <-
function(x) {
s <- 0.0
for(xi in x) s <- s + xi
s
}
kahanSum <- function (x)
{
s <- 0.0
c <- 0.0 # running compensation for lost