Chebyshev-type cubature formulas for doubling weighted spheres, balls, and simplexes

Author:

Dai Feng,Feng Han

Abstract

This paper shows that, given a doubling weight w w on the unit sphere S d 1 \mathbb {S}^{d-1} of R d \mathbb {R}^d , there exists a positive constant K w , d K_{w,d} such that, for each positive integer n n and each integer N max x S d 1 K w , d w ( B ( x , n 1 ) ) N\ge \max _{x\in {\mathbb {S}^{d-1}}} \frac {K_{w,d}} {w(B(x, n^{-1}))} , there exists a set of N N distinct nodes z 1 z_1 , …, z N z_N on S d 1 \mathbb {S}^{d-1} for which ( ) 1 w ( S d 1 ) S d 1 f ( x ) w ( x ) d σ d ( x ) = 1 N j = 1 N f ( z j ) , f Π n d , \begin{equation} \tag {$\ast $} \frac {1}{w({\mathbb {S}^{d-1}})} \int _{{\mathbb {S}^{d-1}}} f(x) w(x)\, d\sigma _d(x)=\frac 1N \sum _{j=1}^N f(z_j),\qquad \forall f\in \Pi _n^d, \end{equation} where d σ d d\sigma _d , B ( x , r ) B(x,r) , and Π n d \Pi _n^d denote the surface Lebesgue measure on S d 1 {\mathbb {S}^{d-1}} , the spherical cap with center x S d 1 x\in \mathbb {S}^{d-1} and radius r > 0 r>0 , and the space of all spherical polynomials of degree at most n n on S d 1 {\mathbb {S}^{d-1}} , respectively, and w ( E ) = E w ( x ) d σ d ( x ) w(E)=\int _E w(x) \, d\sigma _d(x) for E S d 1 E\subset {\mathbb {S}^{d-1}} . If, in addition, w L ( S d 1 ) w\in L^\infty ({\mathbb {S}^{d-1}}) , then the above set of nodes can be chosen to be well separated: \[ min 1 i j N arccos ( z i z j ) c w , d N 1 d 1 > 0. \min _{1\leq i\neq j\leq N}\arccos (z_i\cdot z_j)\geq c_{w,d} N^{-\frac 1{d-1}}>0. \] It is further proved that the minimal number of nodes N n ( w d σ d ) \mathcal {N}_{n} (wd\sigma _d) required in ( \ast ) for a doubling weight w w on S d 1 {\mathbb {S}^{d-1}} satisfies \[ N n ( w d σ d ) max x S d 1 1 w ( B ( x , n 1 ) ) , n = 1 , 2 , . \mathcal {N}_n (wd\sigma _d) \sim \max _{x\in {\mathbb {S}^{d-1}}} \frac 1 {w(B(x, n^{-1}))},\qquad n=1,2,\ldots . \] Proofs of these results rely on new convex partitions of S d 1 {\mathbb {S}^{d-1}} that are regular with respect to a given weight w w and integer N N . Similar results are also established on the unit ball and the standard simplex of R d \mathbb {R}^d .

Our results extend the recent results of Bondarenko, Radchenko, and Viazovska on spherical designs.

Funder

Natural Sciences and Engineering Research Council of Canada

Publisher

American Mathematical Society (AMS)

Subject

Applied Mathematics,General Mathematics

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