# Necessary and sufficient condition for punctual and uniform convergence

• October 16th 2011, 12:14 AM
Lolyta
Necessary and sufficient condition for punctual and uniform convergence
Hello.
Let $h: R\longrightarrow{R}$ and consider $f_n(x)= n(h(x + \frac{1}{n})-h(x))$ find necessary and sufficient condition for:
a) $(f_n)$ is punctual convergent.
b) $(f_n)$ is uniform convergent into bounded intervals.

I appreciate every contribution. Thank you so much.
• October 16th 2011, 05:06 AM
girdav
Re: Necessary and sufficient condition for punctual and uniform convergence
What do we assume on $h$? For example, if h is a discontinuous function such that $h(x+y)=h(x)+h(y)$ for all $x,y\in\mathbb R$, then the function $f_n$ is constant, with a constant which doesn't depend on $n$.
• October 16th 2011, 06:48 AM
Lolyta
Re: Necessary and sufficient condition for punctual and uniform convergence
Quote:

Originally Posted by girdav
What do we assume on $h$? For example, if h is a discontinuous function such that $h(x+y)=h(x)+h(y)$ for all $x,y\in\mathbb R$, then the function $f_n$ is constant, with a constant which doesn't depend on $n$.

We don't assume anything. We are trying to find conditions (for example, h has to be disctontinuos or continious, deribable or not...that kind of things so as to reach a) and b) ).