def qing(ind, k=10.):
    """Qing function defined as:
    $$ f(x) = \sum_{i=1}^{n} (x_i^2 - i)^2$$
    with a search domain of $-500 < x_i < 500, 1 \leq i \leq n$.
    """
    return sum(( (ind[i]**2. - i)**2. for i in range(len(ind)))),