illogical solution. How can i fix it?

i have this code written to solve the system of equations saved in the array (dif) it does everything that i should do but the problem is that whenever i run my program i always get 0 as a solution.

n=input('n=');
E=input('E=');
h=3;
dif=sym(zeros(1,n));
F=0;
x=sym(zeros(1,n));
for k=1:n
    x(k) = sym(sprintf('x%d',k));
end
for i=1:n
    D= 0.5;
%     V=0;
%     b=0;
    for j=1:n
        if (mod(j,2)==0)
           D = D + cos(h*x(j));
        else
           D = D - cos(h*x(j)); 
        end 
    end
    D=(2*E*sqrt(2)/(pi*h))*abs(D);
    F = F + 1/h*(D^2);
    h=h+2;
end
for j=1:n
    dif(j)=diff(F,x(j),1);
end
S=double(solve(dif));
x = structfun(@subs,S)

can anybody tell me what's wrong with this code? thanks in advance.