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Diffeomorphisms with Banach space domains

1992, Nonlinear Analysis: Theory, Methods & Applications

Abstract
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This paper investigates the conditions under which a C1 mapping between Banach spaces can be a global diffeomorphism. The study focuses on sufficient conditions for injectivity and bijectivity, leveraging nonnegative auxiliary scalar coercive functions to establish global properties of the mappings. The results contribute to the understanding of diffeomorphisms in the context of infinite-dimensional spaces.

Key takeaways

  • In this paper we use the hypothesis that the operator norm f ′ (x) −1 is bounded on bounded sets, i.e. sup x ≤r f ′ (x) −1 < +∞ , ∀r : 0 < r < +∞ , (1.2) Theorem 2.1 (in the particular case we mentioned above) says that the local diffeomorphism f is injective if (1.2) holds and there exist a point x 0 ∈ X, and a coercive function k ∈ C 1 (X; R + ), such that
  • We are going to use nonnegative auxiliary scalar coercive functions, that is continuous mappings k : X → R + with k(x) → +∞ as x → +∞ .
  • if conditions (i) and (ii) in Theorem 2.1 are satisfied, and there exist points x 0 , x 1 ∈ X, and nonnegative real numbers a, b, c, such that
  • So (3.2) is satisfied, (3.1) holds by (3.6), and Theorem 3.1 gives Corollary 3.2.
  • The 'if' in Theorem 3.1 and Corollary 3.3 can be substituted by 'if and only if'.