N.diff(i, order=1)

        Derivative wrt index i to given order.

def diff(self, i, order=1):
        """
        N.diff(i, order=1)

        Derivative wrt index i to given order.
        """

        old_val = copy(self[i])
        d = derivative(
            func=self.func_for_diff,
            x0=old_val,
            dx=self.eps[i],
            n=order,
            args=[i],
            order=self.diff_order)
        self[i] = old_val
        return d