From tom@@@k@||ber@ @end|ng |rom gm@||@com  Thu Feb 21 08:55:38 2019
From: tom@@@k@||ber@ @end|ng |rom gm@||@com (Tomas Kalibera)
Date: Thu, 21 Feb 2019 08:55:38 +0100
Subject: [Rd] code for sum function
In-Reply-To: <CAOuLjjRV4cDb73re6JVsMsnVSgBNRdLEPrP=Z6cxSHtnUakUzw@mail.gmail.com>
References: <c1495700-e265-4ff8-1f36-e149bd4d1961@gmail.com>
 <13de2483-4cb0-38eb-4bcc-138844a3c0a8@gmail.com>
 <CAOuLjjRV4cDb73re6JVsMsnVSgBNRdLEPrP=Z6cxSHtnUakUzw@mail.gmail.com>
Message-ID: <71f5408f-faf5-aeeb-76ca-0c4467c57c70@gmail.com>

Dear Rampal,

you can download R source code in form of a tarball or from subversion, 
please see
https://cran.r-project.org/doc/manuals/R-admin.html#Obtaining-R
https://cran.r-project.org/doc/manuals/R-admin.html#Using-Subversion-and-rsync

There is also a web access to subversion, so specifically the sum is 
available in
https://svn.r-project.org/R/trunk/src/main/summary.c

The definition of LDOUBLE is here
https://svn.r-project.org/R/trunk/src/include/Defn.h

The index of R manuals is here
https://cran.r-project.org/manuals.html

The online documentation inside R gives for ?sum
"??? Loss of accuracy can occur when summing values of different signs:
 ???? this can even occur for sufficiently long integer inputs if the
 ???? partial sums would cause integer overflow.? Where possible
 ???? extended-precision accumulators are used, typically well supported
 ???? with C99 and newer, but possibly platform-dependent.
"

Best,
Tomas


On 2/20/19 11:55 PM, Rampal Etienne wrote:
> Dear Tomas,
>
> Where do I find these files? Do they contain the code for the sum 
> function?
>
> What do you mean exactly with your point on long doubles? Where can I 
> find documentation on this?
>
> Cheers, Rampal
>
> On Mon, Feb 18, 2019, 15:38 Tomas Kalibera <tomas.kalibera at gmail.com 
> <mailto:tomas.kalibera at gmail.com> wrote:
>
>     See do_summary() in summary.c, rsum() for doubles. R uses long double
>     type as accumulator on systems where available.
>
>     Best,
>     Tomas
>
>     On 2/14/19 2:08 PM, Rampal Etienne wrote:
>     > Hello,
>     >
>     > I am trying to write FORTRAN code to do the same as some R code I
>     > have. I get (small) differences when using the sum function in R. I
>     > know there are numerical routines to improve precision, but I
>     have not
>     > been able to figure out what algorithm R is using. Does anyone know
>     > this? Or where can I find the code for the sum function?
>     >
>     > Regards,
>     >
>     > Rampal Etienne
>     >
>     > ______________________________________________
>     > R-devel at r-project.org <mailto:R-devel at r-project.org> mailing list
>     > https://stat.ethz.ch/mailman/listinfo/r-devel
>
>


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[Rd] code for sum function
Tomas Kalibera