Matlab global stifness matrix

I have n1 n2 K1= (E*A/L)*[1 -1 n1 -1 1] n2 n2 n3 K2= (E*A/L)*[1 -1; n2 -1 1] n3 n3 n4 K3= (E*A/L)*[1 -1 n3 -1 1] n4 n4 n5 k4= (E*A/L)*[1 -1 n4 -1 1] n5 n5 n6 k5= (E*A/L)*[1 -1 n5 -1 1] n6 n6 n7 K6= (E*A/L)*[1 -1 n6 -1 1] n7

i have to combine the above 6 matrix and form a 7 by 7 global stiffness matrix where the diagonal matrix for expect k11 and k77 will be an addition of the combined nodes of local stiffness matrix.

For. ex. K22=k11+k22 K33=k22+k33 so on...