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# Aubin–Lions lemma

In mathematics, the Aubin–Lions lemma (or theorem) is a result in the theory of Sobolev spaces of Banach space-valued functions, which provides a compactness criterion that is useful in the study of nonlinear evolutionary partial differential equations. Typically, to prove the existence of solutions one first constructs approximate solutions (for example, by a Galerkin method or by mollification of the equation), then uses the compactness lemma to show that there is a convergent subsequence of approximate solutions whose limit is a solution.

The result is named after the French mathematicians Thierry Aubin and Jacques-Louis Lions. In the original proof by Aubin,[1] the spaces X0 and X1 in the statement of the lemma were assumed to be reflexive, but this assumption was removed by Simon,[2] so the result is also referred to as the Aubin–Lions–Simon lemma.[3]

Statement of the lemma

Let *X*_{0}, *X* and *X*_{1} be three Banach spaces with *X*_{0} ⊆ *X* ⊆ *X*_{1}. Suppose that *X*_{0} is compactly embedded in *X* and that *X* is continuously embedded in *X*_{1}. For 1 ≤ *p*, *q* ≤ +∞, let

\( W = \{ u \in L^p ([0, T]; X_0) | \dot{u} \in L^q ([0, T]; X_1) \}. \)(ii) If p = +∞ and q > 1, then the embedding of W into C([0, T]; X) is compact.

(i) If *p* < +∞, then the embedding of *W* into *L ^{p}*([0,

*T*];

*X*) is compact.

(ii) If *p* = +∞ and *q* > 1, then the embedding of *W* into *C*([0, *T*]; *X*) is compact.

Notes

Aubin (1963)

Simon (1986)

Boyer & Fabrie (2013)

References

Aubin, Jean-Pierre (1963). "Un théorème de compacité. (French)". C. R. Acad. Sci. Paris 256. pp. 5042–5044. MR 0152860.

Boyer, Franck; Fabrie, Pierre (2013). Mathematical Tools for the Study of the Incompressible Navier-Stokes Equations and Related Models. Applied Mathematical Sciences 183. New York: Springer. pp. 102–106. ISBN 978-1-4614-5975-0. (Theorem II.5.16)

Lions, J.L. (1969). Quelque methodes de résolution des problemes aux limites non linéaires. Paris: Dunod-Gauth. Vill. MR 259693.

Roubíček, T. (2013). Nonlinear Partial Differential Equations with Applications (2nd ed.). Basel: Birkhäuser. ISBN 978-3-0348-0512-4. (Sect.7.3)

Showalter, Ralph E. (1997). Monotone operators in Banach space and nonlinear partial differential equations. Mathematical Surveys and Monographs 49. Providence, RI: American Mathematical Society. p. 106. ISBN 0-8218-0500-2. MR 1422252. (Proposition III.1.3)

Simon, J. (1986). "Compact sets in the space Lp(O,T;B)". Annali di Matematica Pura ed Applicata 146. pp. 65–96. MR 0916688 (89c:46055).

X.Chen, A.Jungel and J.-G.Liu (2014). "A note on Aubin-Lions-Dubinskii lemmas". Acta Appl. Math. to appear,.

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