element by element solution strategies

[nspk]

I see that a section of member functions of FE_Element Class - the ones pasted below are expected to be used for element by element solution strategies.
I want to know where(in which class) is the element by element strategy implemented since integrators seem to implement the standard full matrix K*X=P.


// methods for ele-by-ele strategies
virtual const Vector &getTangForce(const Vector &x, double fact = 1.0);
virtual const Vector &getK_Force(const Vector &x, double fact = 1.0);
virtual const Vector &getKi_Force(const Vector &x, double fact = 1.0);
virtual const Vector &getC_Force(const Vector &x, double fact = 1.0);
virtual const Vector &getM_Force(const Vector &x, double fact = 1.0);
virtual void addM_Force(const Vector &accel, double fact = 1.0);
virtual void addD_Force(const Vector &vel, double fact = 1.0);