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Equivalence of measures of smoothness in $L_{p}(S^{d-1})$, 1 < p < ∞

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Dai F., Ditzian Z., Huang H.

Studia Mathematica

2010

tom 196

nr 2

179-205

Suppose Δ̃ is the Laplace-Beltrami operator on the sphere $S^{d-1}, Δ^{k}_{ρ}f(x) = Δ_{ρ}Δ^{k-1}_{ρ}f(x)$ and $Δ_{ρ}f(x) = f(ρx) - f(x)$ where ρ ∈ SO(d). Then $ω^{m}(f,t)_{L_{p}(S^{d-1})} ≡ sup{∥Δ^{m}_{ρ}f∥_{L_{p}(S^{d-1})}: ρ ∈ SO(d), max_{x∈ S^{d-1}} ρx·x ≥ cos t}$ and $K̃ₘ(f,t^{m})_{p} ≡ inf{∥f - g∥_{L_{p}(S^{d-1})} + t^{m}∥(-Δ̃)^{m/2}g∥_{L_{p}(S^{d-1})}: g ∈ 𝓓((-Δ̃)^{m/2})}$ are equivalent for 1 < p < ∞. We note that for even m the relation was recently investigated by the second author. The equivalence yields an extension of the results on sharp Jackson inequalities on the sphere. A new strong converse inequality for $L_{p}(S^{d-1})$ given in this paper plays a significant role in the proof.

Ograniczanie wyników

1 Studia Mathematica

1 Dai F.

1 Ditzian Z.

1 Huang H.

1 2010

Wyniki wyszukiwania

Equivalence of measures of smoothness in $L_{p}(S^{d-1})$, 1 < p < ∞