Hi all, i am trying to compile a test, calling from C code R Lapack shared
libraries. In particular, i am calling simple LAPACK driver
dposv for solving linear equation system A*x=B with positive definite A. My
code looks like the following in
solve.c
==========================
#include<stdio.h>
#include <R_ext/BLAS.h>
#include <R_ext/Lapack.h>
int main(){
double A[4]={1,0.5,0.5,1};
double B[2]={3,4};
char uplo='U';
int n = 2, nrhs=1, lda=2, ldb=2, info, i;
F77_CALL(dposv)(&uplo,&n, &nrhs, A, &lda, B, &ldb,
&info);
for(i=0; i<2; i++){
printf("%f\n", B[i]);
}
return info;
}
==========================
When I am trying to link to BLAS/LAPACK using
gcc -std=gnu99 solve.c -o test -I$R_HOME/include -L$R_HOME/lib -lRblas -lRlapack
-lgfortran
linker generates an error message
$RHOME/lib/libRblas.so: undefined reference to `xerbla_'
Dumping symbol table shows that indeed libRblas.so has undefined xerbla_ symbol
and so does libRlapack. Confusingly, documentation says that xerbla is error
checking routine for BLAS, but it is not found in the library libRblas.
I did find out that xerbla is defined in libR.so and when i link to R library,
everything seems to go fine. However, i have a nagging feeling i am doing
something wrong. It doesn't make sense to me that i cannot compile code
that
doesn't use R without linking to R. Also, one would want to switch
transparently between different implementations of BLAS for example for testing
purposes and not modify linking instructions. Would appreciate if someone with
better understanding of R commented on how to properly link to BLAS and LAPACK
libraries included with R.
