[R] 0/0, R segfaults

[Prof Brian Ripley]

To expand on Dirk's answer, R relies on fairly close compliance to 
IEC60559 (aka IEEE754) arithmetic in which 0/0 = NaN.  As R is C/Fortran 
program, this is a function of your C/Fortran compilers (it is most likely 
an FPU setting controlled by the compiler than libc).  Problems in this 
area are documented in the R-admin manual.

We don't know the CPU here, so ix86 is a plausible guess.  That has a FPU
control word that determines if 0/0 is NaN or an exception.  Prior to 
glibc 2.1 it could be set by __setfpucw and R sets it if NEED___SETFPUCW
is defined (only in older Linuxen).

Other people using Gentoo are not reporting problems, so this has to be a 
very specific problem, one which is best addressed to a Gentoo list.  Try 
a very simple C program such as

#include <stdio.h>
int main()
{
    double x = 0.0;
    printf("x/x = %f\n", x/x); 
}

R is doing nothing different on my Linux box (except it arranges to print 
NaN not nan regardless of platform).

On Thu, 18 Aug 2005, Dirk Eddelbuettel wrote:

>
> On 18 August 2005 at 16:01, Xing Qiu wrote:
> | Hi,
> |
> |     I noticed that when I was conducting some calculation involving
> | finding correlation coeficients, R stopped abnormally. So I did some
> | research, and find out that 0/0 was the culprit.  For sure 0/0 is not
> | a valid expression, but R should give a warning, an error msg or NaN
> | instead of segmentation fault.
> |
> |     I am using R 2.1.0 under Gentoo Linux. My GCC version is 3.3.5.
>
> edd at basebud:~> R
>
> R : Copyright 2005, The R Foundation for Statistical Computing
> Version 2.1.1  (2005-06-20), ISBN 3-900051-07-0
>
> R is free software and comes with ABSOLUTELY NO WARRANTY.
> You are welcome to redistribute it under certain conditions.
> Type 'license()' or 'licence()' for distribution details.
>
> R is a collaborative project with many contributors.
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>
> Type 'demo()' for some demos, 'help()' for on-line help, or
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> Type 'q()' to quit R.
>
>> 0/0
> [1] NaN
>>
>
> No problem on Debian 'testing' with R 2.1.1. You may want to try a different
> libc.
>
> Dirk
>
> -- 
> Statistics: The (futile) attempt to offer certainty about uncertainty.
>         -- Roger Koenker, 'Dictionary of Received Ideas of Statistics'
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595