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Exercise

Boiler plate

As you saw in the previous exercise, the code below does not compile. 

#include <Rcpp.h>
using namespace Rcpp ; 

double twice(double x){
    return x + x
}

Let's modify it.

Instructions
100 XP
  • Fix the syntax error on the function's return line (line 8).
  • Add an [[Rcpp::export]] decorator so that the function is exported to R.