A mapping f over a complete metric space (U, d) is said to be contractive iff there exists an a < 1 such that for any two points x, y an element of U, the distance d (f(x), f(y)) <= a centre dot d (x, y). Banach's fixed-point theorem [1] ensures that if f is contractive, the sequence converges to a point x_f that depends only on f and not on the initial point x. The point x_f is said to be the attractor of f.
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