Wk = zeros(N);
Vk = V(x) + VH(x);
tic;
for k1=1:N
    for k2=1:N
        Wk(k1,k2) = w * (B(k1,:) .* Vk.' .* B(k2,:)).';
    end
end
fprintf('ohne Beachtung der Symmetrie: %s\n', szeit(toc));

Wk1 = zeros(N);
tic;
for k1=1:N
    Wk1(k1,k1) = w * (B(k1,:).^2 .* Vk.').';
    for k2=k1+1:N
        Wk1(k1,k2) = w * (B(k1,:) .* Vk.' .* B(k2,:)).';
        Wk1(k2,k1) = Wk1(k1,k2);
    end
end
fprintf('mit  Beachtung der Symmetrie: %s\n', szeit(toc));
serr(Wk, Wk1);