/****************************/
#include<valarray>
using namespace std;

class mvector : public valarray<double>
{
public:
mvector();
mvector(int size);
};

mvector::mvector() : valarray<double>() {}
mvector::mvector(int size): valarray<double>(size){}

int main()
{
   mvector v(3);  
   v = (mvector&)(v + 2.0);
}