Hi,
Has anyone encountered the problem of rgamma function in C? The
following simplified program always dies for me, and I wonder if anyone
can tell me the reason.
#include <Rmath.h>
#include <time.h>
#include <Rinternals.h>
SEXP generateGamma ()
{
srand(time(NULL));
return (rgamma(5000,1));
}
Has anyone encountered a similar problem before? Is there another way of
generating Gamma random variable in C?
P.S. I have no problem compiling and loading this function in R.
Thanks for suggestions in advance!
--Chandler
On Jul 14, 2012, at 04:55 , Chandler Zuo wrote:> Hi, > > Has anyone encountered the problem of rgamma function in C? The following simplified program always dies for me, and I wonder if anyone can tell me the reason. > > #include <Rmath.h> > #include <time.h> > #include <Rinternals.h> > > SEXP generateGamma () > { > srand(time(NULL)); > return (rgamma(5000,1)); > } > > Has anyone encountered a similar problem before? Is there another way of generating Gamma random variable in C? > > P.S. I have no problem compiling and loading this function in R.It doesn't even give off a warning?? The prototype in Rmath.h is double rgamma(double, double); and you should be returning an SEXP. As soon as something tries to interpret the double value as a pointer -- Poof! Notice that rgamma in C is not the same function as the R counterpart, in particular it isn't vectorized, so only generates one random number at a time. The long and the short of it is that you need to read up on sections 5.9 and 5.10 of Writing R Extensions.> > Thanks for suggestions in advance! > > --Chandler > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code.-- Peter Dalgaard, Professor, Center for Statistics, Copenhagen Business School Solbjerg Plads 3, 2000 Frederiksberg, Denmark Phone: (+45)38153501 Email: pd.mes at cbs.dk Priv: PDalgd at gmail.com
On Fri, Jul 13, 2012 at 7:55 PM, Chandler Zuo <zuo at stat.wisc.edu> wrote:> Hi, > > Has anyone encountered the problem of rgamma function in C? The following > simplified program always dies for me, and I wonder if anyone can tell me > the reason. > > #include <Rmath.h> > #include <time.h> > #include <Rinternals.h> > > SEXP generateGamma () > { > srand(time(NULL)); > return (rgamma(5000,1)); > }rgamma doesn't return an SEXP, it returns a double. Also, the srand() call is pointless.> Has anyone encountered a similar problem before? Is there another way of > generating Gamma random variable in C? > > P.S. I have no problem compiling and loading this function in R.Strange. You should get compiler warnings that the return type is incompatible. I get foo.c: In function ?generateGamma?: foo.c:7: warning: implicit declaration of function ?srand? foo.c:8: error: incompatible types in return I thought the ANSI standard actually *required* a diagnostic for the incompatible return types. -thomas -- Thomas Lumley Professor of Biostatistics University of Auckland