In R this would be A%*%B.  In Rcpp it is matmul(A,B).

### Calls function: dot

Rcpp::NumericMatrix matmul(Rcpp::NumericMatrix A,Rcpp::NumericMatrix B)
   {     int a= A.nrow();
         int b= B.ncol();
         Rcpp::NumericMatrix C(a,b);
         for (int i = 0; i < a; i++)
         {  for (int j = 0; j < b; j++)
            {   C(i,j)= dot(A(i,_),B(_,j));
            }
         }
         return C;
   }