Besov space

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In mathematics, the Besov space (named after Oleg Vladimirovich Besov) B^s_{p,q}(\mathbf{R}) is a complete quasinormed space which is a Banach space when 1 ≤ p, q ≤ ∞. It, as well as the similarly defined Triebel–Lizorkin space, serve to generalize more elementary function spaces and are effective at measuring (in a sense) smoothness properties of functions.

Definition[edit]

Let

 \Delta_h f(x) = f(x-h) - f(x)

and the modulus of continuity is defined by

 \omega^2_p(f,t) = \sup_{|h| \le t} \left \| \Delta^2_h f \right \|_p

Let n be a non-negative integer and define: s = n + α with 0 < α ≤ 1, the Besov space B^s_{p,q}(\mathbf{R}) contains all functions f such that

 f \in W^{n, p}(\mathbf{R}), \qquad \int_0^\infty \left|\frac{ \omega^2_p \left ( f^{(n)},t \right ) } {t^{\alpha} }\right|^q \frac{dt}{t} < \infty.

Norm[edit]

The Besov space B^s_{p,q}(\mathbf{R}) is equipped with the norm

 \left \|f \right \|_{B^s_{p,q}(\mathbf{R})} = \left( \|f\|_{W^{n, p} (\mathbf{R})}^q + \int_0^\infty \left|\frac{ \omega^2_p \left ( f^{(n)}, t \right ) } {t^{\alpha} }\right|^q \frac{dt}{t} \right)^{\frac{1}{q}}

The Besov spaces B^s_{2,2}(\mathbf{R}) coincide with the more classical Sobolev spaces H^s(\mathbf{R}).

References[edit]

  • Triebel, H. "Theory of Function Spaces II".
  • Besov, O. V. "On a certain family of functional spaces. Embedding and extension theorems", Dokl. Akad. Nauk SSSR 126 (1959), 1163–1165.
  • DeVore, R. and Lorentz, G. "Constructive Approximation", 1993.
  • Weisstein, Eric W. "Besov Space." From MathWorld—A Wolfram Web Resource. http://mathworld.wolfram.com/BesovSpace.html
  • DeVore, R., Kyriazis, G. and Wang, P. "Multiscale characterizations of Besov spaces on bounded domains", Journal of Approximation Theory 93, 273-292 (1998).