def f_a(self, k, m, A):
raise NotImplemented("<STR_LIT>")<EOL>
p_a: function (k, x_{k-1}, A_{k}). Dynamic function.
    k (iteration number), starts at 0
    x_{k-1} State from the previous step
    A_{k} Jacobian matrices of f_a. In the linear case it is exactly
    A_{k}.