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单词 BestApproximation
释义

best approximation


One of the problems in approximation theory is to determine points that minimize distances (to a given point or subset). More precisely,

Problem - Let X be a metric space and SX a subset. Given x0X we want to know if there exists a point in S that minimizes the distance to x0, i.e. if there exists y0S such that

d(x0,y0)=infySd(x0,y)

Definition - A point y0 that the above conditions is called a best approximation of x0 in S.

In general, best approximations do not exist. Thus, the problem is usually to identify classes of spaces X and S where the existence of best approximations can be assured.

Example : When S is compact, best approximations of a given point x0X in S always exist.

After one assures the existence of a best approximation, one can question about its uniqueness and how to calculate it explicitly.

Remark - There is no reason to restrict to metric spaces. The definition of best approximation can be given for pseudo-metric spaces, semimetric spaces or any other space where a suitable notion of ”distance” can be given.

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更新时间:2025/5/4 12:29:30