function foo (x, arr, T)
    n = length(arr);
    y = zeros(1, length(x)) + arr(1) / 2;
    t = 1;
    for k = [2:n]
        t /= 2;
        y += arr(k) * t * cos(2 * pi * k * x / T);
    end
    figure();
    plot(x, y);
end