View source for Lp spaces

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{{MSC|46E30}}

In functional analysis, an $L^p$ space is a space of functions for which the $p$-th power of their absolute value is Lebesgue integrable. $L^p$ spaces are sometimes called ''Lebesgue spaces''.

More precisely, let $(S, F, \mu)$ be a $\sigma$-finite measure space with $S$ the space, $F$ the $\sigma$-algebra of  measurable sets and $\mu$ the measure. If the power is in the interval $1\le p \lt \infty$, then the  $L^p$ space $L^p(S, F, \mu)$ contains the equivalence classes of complex measurable functions for which
$$
\int_S |f(s)|^p \; d\mu(s) < \infty
$$
where two functions $f$ and $g$ are equivalent if $f=g$ almost everywhere with respect to $\mu$.[[#References|[1]]]

The $L^p$ norm of $f$ for $1\le p \lt \infty$ is 
$$
\| f \|_p  = \left( \int_S |f(s)|^p \; d\mu(s) < \infty \right)^{1/p}
$$

For $p = \infty$,  $L^\infty$ space $L^p(S, F, \mu)$ consists of all the equivalence classes of measurable functions on $S$ such that for a positive constant $M < \infty$,
$$
|f(s)| < M
$$
almost everywhere with respect to $\mu$.[[#References|[1]]]

For $0\lt p \lt 1$, the $L^p$ norm does not satisfy the triangle inequality.[[#References|[1]]]

== References ==
[1] Stein, Elias M.; Shakarchi, Rami (2011). Functional Analysis: Introduction to Further Topics in Analysis. Chapter 1, Princeton University Press. ISBN 9780691113876.