There is no way to do that, because when the base class constructor is run, the object is not yet an object of the derived type. In particular, data members introduced in the derived class are not initialised until after the base class constructor is run -- in essence, the base class object behaves like a data member of the derived class.
One way or another, you will have to defer the calculation until the derived class's constructor is entered. If I understand what you're trying to do correctly, the best way is probably to give the base class a member function that does the calculations and call that from the derived classes' constructors.
