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If M is non-empty compact set, then the metric projection p M is upper semi-continuous, but might not be lower semi-continuous. But if X is a normed space and M is a finite-dimensional Chebyshev set, then p M is continuous. [citation needed] Moreover, if X is a Hilbert space and M is closed and convex, then p M is Lipschitz continuous with ...
Hausdorff and Gromov–Hausdorff distance define metrics on the set of compact subsets of a metric space and the set of compact metric spaces, respectively. Suppose (M, d) is a metric space, and let S be a subset of M. The distance from S to a point x of M is, informally, the distance from x to the closest point of S.
The product of a finite set of metric spaces in Met is a metric space that has the cartesian product of the spaces as its points; the distance in the product space is given by the supremum of the distances in the base spaces. That is, it is the product metric with the sup norm. However, the product of an infinite set of metric spaces may not ...
In topology and related areas of mathematics, a metrizable space is a topological space that is homeomorphic to a metric space.That is, a topological space (,) is said to be metrizable if there is a metric: [,) such that the topology induced by is . [1] [2] Metrization theorems are theorems that give sufficient conditions for a topological space to be metrizable.
Let (,) be a metric space, where is a given set. For any point and any non-empty subset , define the distance between the point and the subset: (,):= (,),.For any sequence of subsets {} = of , the Kuratowski limit inferior (or lower closed limit) of as ; is := {:,} = {: (,) =}; the Kuratowski limit superior (or upper closed limit) of as ; is := {:,} = {: (,) =}; If the Kuratowski limits ...
Let X and Y be two metric spaces, and F a family of functions from X to Y.We shall denote by d the respective metrics of these spaces.. The family F is equicontinuous at a point x 0 ∈ X if for every ε > 0, there exists a δ > 0 such that d(ƒ(x 0), ƒ(x)) < ε for all ƒ ∈ F and all x such that d(x 0, x) < δ.
Thus metric spaces together with metric maps form a category Met. Met is a subcategory of the category of metric spaces and Lipschitz functions. A map between metric spaces is an isometry if and only if it is a bijective metric map whose inverse is also a metric map. Thus the isomorphisms in Met are precisely the isometries.
An arc is a space homeomorphic to the closed interval [0,1]. If h: [0,1] → X is a homeomorphism and h(0) = p and h(1) = q then p and q are called the endpoints of X; one also says that X is an arc from p to q.