[Rd] The following code (using rgamma) hangs
Faheem Mitha
faheem at faheem.info
Fri Jan 27 22:03:05 CET 2012
Hi,
I'm seeing something that may be a bug in R's standalone math library,
which is packaged by Debian as r-mathlib. I reported it to the Debian BTS
as http://bugs.debian.org/657573
I'm using Debian squeeze, and the code was tested with r-mathlib 2.11.1-6
(default on stable) and 2.14.1-1 (from testing/unstable).
I summarize this report below. The following code with the R math library
hangs. Note that set_seed is defined as taking two unsigned int arguments,
so 0's are valid arguments. I'm guessing that since 0 is as low as an
unsigned integer can go, it represents some kind of edge case.
################################################
#define MATHLIB_STANDALONE
#include <Rmath.h>
int main(void)
{
set_seed(0, 0);
rgamma(1, 1);
}
################################################
If I add the definitions of `get_seed` and `set_seed` from
`src/nmath/standalone/sunif.c` to my code, then the hang disappears.
################################################
#define MATHLIB_STANDALONE
#include <Rmath.h>
/* A version of Marsaglia-MultiCarry */
static unsigned int I1=1234, I2=5678;
void set_seed(unsigned int i1, unsigned int i2)
{
I1 = i1; I2 = i2;
}
void get_seed(unsigned int *i1, unsigned int *i2)
{
*i1 = I1; *i2 = I2;
}
int main(void)
{
set_seed(0, 0);
rgamma(1, 1);
}
################################################
I assume sunif.c defines the `get_seed` and `set_seed` for the R
standalone random number generation facilities.
However, I wonder why
a) redefining them in my source file makes the hang go away
and
b) why doesn't redefining `get_seed` and `set_seed` (even with the same
definition) give a linker error, since the function has been defined in
the library already?
Dirk also pointed out (in the bug report) that you get the following
##########################################################
int main(void)
{
set_seed(0, 0);
cout << "one normal " << norm_rand() << endl;
}
##########################################################
edd at max:/tmp$ g++ -o faheem faheem.cpp -lRmath; ./faheem
one normal -inf
One would expect norm_rand to return finite values, even in edge cases.
If you want me to report this as a bug, let me know. Thanks.
Regards, Faheem
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