0/0, R segfaults

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

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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'