Trudinger's theorem
# Trudinger's theorem

In mathematical analysis, Trudinger's theorem or the Trudinger inequality (also sometimes called the Moser–Trudinger inequality) is a result of functional analysis on Sobolev spaces. It is named after Neil Trudinger (and Jürgen Moser).

It provides an inequality between a certain Sobolev space norm and an Orlicz space norm of a function. The inequality is a limiting case of Sobolev imbedding and can be stated as the following theorem:

Let $\Omega$ be a bounded domain in $\mathbb {R} ^{n}$ satisfying the cone condition. Let $mp=n$ and $p>1$. Set

    $A(t)=\exp \left(t^{n/(n-m)}\right)-1.$

Then there exists the embedding

    $W^{m,p}(\Omega )\hookrightarrow L_{A}(\Omega )$

where

    $L_{A}(\Omega )=\left\{u\in M_{f}(\Omega ):\|u\|_{A,\Omega }=\inf\{k>0:\int _{\Omega }A\left({\frac {|u(x)|}{k}}\right)~dx\leq 1\}<\infty \right\}.$

The space

    $L_{A}(\Omega )$

is an example of an Orlicz space.

