Let f : X → Y be a mapping from set X to set Y. That is, suppose that for each point x in X there corresponds a point f ( x ) in Y. If both sets X and Y have a structure that can be expressed by concepts such as "close" or "approaching", i.e. a topological structure, then we can define the concept that the mapping f is continuous at point a in X. In other words, we define it by the condition that "if point x in X is close to a , then f ( x ) will be as close as possible to f ( a )." Then, by defining it as "if f is continuous at each point in X , then the mapping f : X → Y is continuous," we obtain the concept of a continuous mapping. Source: Heibonsha World Encyclopedia, 2nd Edition Information |
f:X→Yを集合Xから集合Yへの写像とする。すなわちXの各点xに対しYの点f(x)が対応しているとする。もし集合X,Yのいずれもが“近い”とか“近づく”といった概念で表される構造,すなわち位相構造を備えていれば,写像fがXの点aで連続であるという概念が定義できる。すなわち,〈Xの点xがaに近くなれば,f(x)がf(a)にいくらでも近くなる〉という条件によってそれを定義するのである。そして,〈fがXの各点で連続であるとき,写像f:X→Yは連続である〉と定義することにより,連続写像という概念が得られる。
出典 株式会社平凡社世界大百科事典 第2版について 情報 |
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