%Establish Mass Matrix
mass = 90;  %kg
zg = 0.9656;

 = zeros(6,6);
M(1,1) = mass;
M(2,2) = mass;
M(3,3) = mass;
M(5,1) = -mass*zg;
M(1,5) = -mass*zg;
M(4,2) = mass*zg;
M(2,4) = mass*zg;

m = mass;
A = 1;

xi3 = A*F{7,3}/(-w.^2*(m-F{3,3})