For a 2DOF:

                                                    (30)

Similarly    

                                                                         (31)

Weighted Model Matrix : If each column of the model matrix P is divided by the square root of the generalized mass M_i , the new matrix is called weighted model matrix and designated as .

So and                                                                              (32)

Here I is the unity matrix and matrix is a diagonal matrix with eigenvalues in the diagonal elements.