The Weierstrass approximation theorem states that any continuous function f:I→R on a closed, bounded, connected subset I⊆R can be ... ... <看更多>
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weierstrass approximation theorem 在 topology.continuous_function.weierstrass - mathlib docs 的推薦與評價
The Weierstrass approximation theorem for continuous functions on `[a,b]`. We've already proved the Weierstrass approximation theorem in the sense that ... ... <看更多>
weierstrass approximation theorem 在 [分析] Weierstrass approximation theorem - 看板Math - 批踢踢 ... 的推薦與評價
早安!有個問題想請教大家,謝謝。
關於Weierstrass approximation theorem,Rudin(Theorem 7.26)是這麼陳述的:
If f\in C[a,b], there is a sequence <P_n>_{n=1}^{∞} of polynomials such
that P_n→f uniformly on [a,b].
※ C[a,b] denotes the set of all continuous functions defined on the closed
interval [a,b].
但我在Apostol(Theorem 11.17)跟"數學傳播"的某篇文章(好像是林琦焜老師還是
劉豐哲老師)看到另一種敘述:
If f\in C[a,b], then for every ε>0, there is a polynomial P such that
|P(x)-f(x)|<ε whenever x\in [a,b].
我在想是否能證明等價或至少證明一個方向的implication,現在看來,sequence版本
可以導出one-polynomial版本,只要將uniform convergence的定義打開並取足夠後面
的項即可,但另一個方向我就不確定了,不知該如何用P造出符合uniform convergence
的P_n
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謝謝...
※ 編輯: cyt147 (180.177.114.46), 06/08/2018 08:43:27
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