I am looking for some interesting examples of sequences of functions/of derivatives which satisfy the follwoing conditions:
- $f_n'(x)$ must converge pointwisely,
- $f_(x)$ should converge uniformly or pointwisely,
- $\lim_{n\to\infty}f_n'(x)\neq \left(\lim_{n\to\infty}f_n(x)\right)'$.
So far I have only found:
$f_n:[0,1]\to\mathbb{R}$, where $f_n(x)= \frac{1}{n}x^n$ and $f_n'(x)=x^{n-1}$.
In this case:
$$\left(\lim_{n\to\infty}f_n(x)=\hat{0}\right)'=\hat{0} \neq \lim_{n\to\infty}f_n'(x)= \begin{cases} 1, \text{if } x \ne 1 \\ 0, \text{else. } \end{cases} $$
Maybe someone has some more examples to share :)
EDIT
Maybe it is possible to find an example where the limit of $f_n'(x)$ attains a "nice" form, e.g. a polynomial or an elementary function without the necessity of defining it piecewise where you have jumps.