how to get beta function in rcpp

Question

I need to use beta function Beta(a, b) in my calculation in Rcpp. A simple code example I wrote is here:

cppFunction('double getbeta(double a, double b){
  double res = beta(a, b);
  return res;
}')

But I got an error in R saying that

no matching function for call to 'beta'

Is it because we cannot use Beta function in Rcpp? If we could, is there the corresponding function

lbeta 

can be used?

Answer 1

Use the R:: namespace for the scalar-value functions (and Rcpp:: for vectorised sugar functions):

R> library(Rcpp)
R> cppFunction('double getbeta(double a, double b){
+   double res = R::beta(a, b);
+   return res;
+ }')
R> getbeta(1.0, 2.0)
[1] 0.5
R>