Zeitschrift für Analysis und ihre Anwendungen
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Published online: 1997-09-30
Differentiability Properties of the Autonomous Composition Operator in Sobolev SpacesMassimo Lanza de Cristoforis (1) Università di Padova, Italy
In this paper, we study the autonomous composition operator, which takes a pair of functions $(f,g)$ into its composite function $f\ o \ g$. We assume that $f$ and $g$ belong to Sobolev spaces defined on open subsets of $\mathbb R^n$, and we concentrate on the case in which the space for $g$ is a Banach algebra. We give a sufficient condition in order that the composition maps bounded sets to bounded sets, and we exploit the density of the polynomial functions in the space for I in order to prove that for suitable Sobolev exponents of the spaces for $f$ and $g$, the composition is continuous and differentiable with continuity up to order $r$, with $r ≥ 1$. Then we show the optimality of such conditions by means of theorems of ’inverse’ type.
Keywords: Superposition operators, nonlinear operators, Sobolev spaces
Lanza de Cristoforis Massimo: Differentiability Properties of the Autonomous Composition Operator in Sobolev Spaces. Z. Anal. Anwend. 16 (1997), 631-651. doi: 10.4171/ZAA/782