Pointwise Christoffel function estimate for two-dimensional [?][?]-balls

Let 1<α<21<\alpha<2 and let xBα2{\boldsymbol{x}}\in B^2_\alpha. Define

δ:=dist(x,Bα2),li:=max{t:x+(1)itvBα2},i=1,2,\delta:={\rm dist}({\boldsymbol{x}},\partial B^2_\alpha),\qquad l_i:=\max\{t:{\boldsymbol{x}}+(-1)^it{\boldsymbol{v}}\in B^2_\alpha\},\quad i=1,2,

where u{\boldsymbol{u}} satisfies x+δuD{\boldsymbol{x}}+\delta{\boldsymbol{u}}\in\partial D and v{\boldsymbol{v}} is one of the two unit vectors orthogonal to u{\boldsymbol{u}}. Pointwise Christoffel function conjecture. If δ>σn2\delta>\sigma n^{-2}, with σ>0\sigma>0, then

λn(Bα2,x)c(α,σ)n2l1l2.\lambda_n(B^2_\alpha,{\boldsymbol{x}})\approx c(\alpha,\sigma)n^{-2}\sqrt{l_1l_2}.

The preceding discussion establishes analogous estimates at singular and smooth boundary points, while the general pointwise behavior away from the diagonal direction is posed as an interesting problem; the source does not provide a resolution of this assertion.

Sources & referencesView supporting material

Primary source

A. Prymak, “Upper estimates of Christoffel function on convex domains”, arXiv:1704.03025 (2017).

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