G2.m

function [sum ] = G(l1,l2,x,f,m1,m2,g)
    
    sum=(m1+m2)*l1*f(3)...
        +m2*l2*f(4)*cos(x(1)-x(2))...
        +m2*l2*f(2)^2*sin(x(1)-x(2))...
        +g*(m1+m2)*sin(x(1));
end