Function fixed_point_systems(x0, N) approximates the solution of a system of nonlinear equations F(x) = (f1(x), f2(x), ..., fn(x)) = 0 rewritten in the fixed-point form x = G(x) = (g1(x), g2(x), ..., gn(x)). This is done by the user at the bottom of the file. The sub-function G(x) has to be updated accordingly with the given system. The iteration scheme x(k+1) = G(x(k)) is implemented until condition |x(k) - x(k-1)| < tol is met, starting with an initial approxiamtion vector x0. If, after N iterations, the stopping criterion is not reached, a message concerning the iterated x's is displayed. the output consists of iterates of each variables x1, x2, ..., xn in each column.