Hi,
I'm simulating a Markov chain in Fortran interfaced with R-2.2.1 in order
to generate data according to a Markov Random Field called the Potts model.
R Version:
platform i686-pc-linux-gnu
arch i686
os linux-gnu
system i686, linux-gnu
status
major 2
minor 2.1
year 2005
month 12
day 20
svn rev 36812
Each loop of my Fortran calls the function rmultinom.c of the R's Random
Number Generator through the wrapper:
#include <R.h>
#include <Rmath.h>
void F77_SUB(sarmultinom)(int n,
double* prob,
int K,
int* rN){
rmultinom(n, prob, K, rN);}
My fortran program is:
subroutine testsarmultinom(n,prob,K,rN)
implicit none
integer n,K,rN(K)
double precision prob(K)
call rndstart()
call sarmultinom(n,prob,K,rN)
call rndend()
end
In order to understand better how the function rmultinom.c works, I have
written an R code which calls this fortran subroutine as follows:
system("R CMD SHLIB test-multinom.f wrapper.c")
dyn.load("~/Package/test/test-multinom.so")
n=1
prob=c(0.6,0.1,0.3)
K=3
rN=c(1,0,0)
res<- .Fortran("testsarmultinom",
as.integer(n),
as.double(prob),
as.integer(K),
as.integer(rN))
Unfortunately, I have some trouble with the results. First, this command
always returns 0 values. In other words, I always get:
>res[[4]]
[1] 0 0 0
Moreover, if I run this R code a second time, an error message appears:
Segmentation fault.
Has somebody ever used rmultinom.c and encountered these problems? My code
must be wrong but I don't know where. In this case, what is the correct way
to call the C function rmultinom.c?
Thanks in advance,
Sophie.
Sophie Ancelet
ENGREF
Laboratoire Grese
19 avenue du Maine
75 732 Paris Cedex 15
France
tel: 33 1 45 49 89 27
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