Parallel Computing for Data Science

5.5. EXAMPLE: ADJACENCY MATRIX, R-CALLABLE CODE 135

The file y.c must include the R header file:

#include <R.h>

Generally the good thing about compiling via R CMD SHLIB is that we

don’t have to worry where the header file is, or worry about the library

files. But things are a bit more complicated if one’s code uses OpenMP, in

which case we must so inform the compiler. We can do this by setting the

proper environment variable. For C code and the bash shell, for instance,

we would issue the shell command

% e x p o r t SHLIB OPENMP CFLAGS = −fopenmp

Here is a sample run, again in the R interactive shell, with the C file being

AdjMatXformForR.c:

n <− 5

dyn . lo