Stuck on MDOF Vibrations problem

This is the Question I am trying to look at. "Derive the equations of motion for a model 10-story building. Assume that each floor has a mass of m=1kg, an inter-story shear stiffness of k=500N/m, and that there is no inter-story damping. Label the horizontal coordinates of horizontal story deflection as x1to x10., where x1 is the displacement of the first floor and x10 is the displacement of the 10th floor.Assume that there is horizontal base motion y(t)below the first floor, presumably modeling ground motion during an earthquake. b. Compute the natural frequencies of the building, and plot the first three mode shapes.

I have done the first aprt by hand and I think I got it. But I am having trouble writing the code for the send part. This is what I have so far,

m=1; k=500; M=eye(10,10)*m; K=[2 -1 0 0 0 0 0 0 0 0 ; -1 2 -1 0 0 0 0 0 0 0 ; 0 -1 2 -1 0 0 0 0 0 0 ; 0 0 -1 2 -1 0 0 0 0 0 ; 0 0 0 -1 2 -1 0 0 0 0 ; 0 0 0 0 -1 2 -1 0 0 0 ; 0 0 0 0 0 -1 2 -1 0 0 ; 0 0 0 0 0 0 -1 2 -1 0 ; 0 0 0 0 0 0 0 -1 2 -1 ; 0 0 0 0 0 0 0 0 -1 1]*k; Kt=(M^(-1/2))*K*(M^(-1/2)) [P,L]=eig(Kt) w1=sqrt(L(1,1)) w2=sqrt(L(2,2)) w3=sqrt(L(3,3)) w4=sqrt(L(4,4)) w5=sqrt(L(5,5)) w6=sqrt(L(6,6)) w7=sqrt(L(7,7)) w8=sqrt(L(8,8)) w9=sqrt(L(9,9)) w10=sqrt(L(10,10))

As you can see i hand typed the stiffness matrix (which I know looks dumb, but it was the only way I could guarantee it was right). I need help with the next part, and I think im right with the eig commands and such.

Thanks for anything