2
$\begingroup$

How to prove the metric space $L^{p}[a,b]$ is a complete metric space using the definition that says, Every Cauchy sequence in the metric space should converge to some point in that space? $\left\{x(t)\in C[a,b] : \int_a^b |x(t)|^p \;dt < \infty \right\};$ $||x(t)||=\left[\int_a^b|x(t)|^p \;dt\right]^\frac{1}{p}$

  • 0
    In that case it is complete by definition.2011-12-19

2 Answers 2

1

Have you tried searching the internet. These are standard questions in functional analysis. You can find an answer at the below link.

  • 0
    thank you for your response.2011-12-19
1

Per t.b.'s comment, your space isn't $L^p[a,b]$. $L^p[a,b]$ is the space of measurable functions that are $p$-integrable over $[a,b]$ ( $\int_a^b |f|^p<\infty$).

That these spaces are complete is known, to some, as the Riesz-Fischer theorem. The standard proof of this theorem uses the fact that a normed space is a Banach Space if and only if every absolutely summable series is summable.

If you want a proof that $L_p$ is complete, without using the above fact ("using Cauchy sequences", as you ask), see here (this proof essentially incorporates that fact, though).

  • 0
    Thank you for your kind and quick response!2011-12-19