4
$\begingroup$

Can anyone provide an example of a sequence $(x_{k}) \in L^p(\mathbb{N})$ with $1 such that $x_{k}(n)\rightarrow 0$ as $k\rightarrow \infty$ such $x_{k}$ doesn't converges weakly to zero.

The sequence has to be unbounded because if the sequence is bounded with this the sequence is weakly convergent.

1 Answers 1

5

Weakly convergent sequences are norm bounded, so any unbounded sequence will work.

For an explicit example in $\ell_2$, take $x_n=ne_n$, where $e_n$ is 0 in all coordinates save the $n$'th, which is 1. Then the functional $x^*=(1,1/2,1/3,\ldots)$ verifies that $(x_n)$ is not weakly convergent to the zero vector (and thus not weakly convergent).

Similar examples can be constructed for other $\ell_p$ spaces.

  • 0
    The same example holds for $\ell_{p}$. Including the same functional. Thanks for clearing it up!2012-02-25