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daxiaobing

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[求助] 连续函数介值定理 几何推广已有1人参与

求助:几何中有没有类似连续函数介值定理这样的结论,大概就是:连续曲线从区域(未必单连通)外到区域内部,是否一定经过边界?谢谢!
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zaq123321

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【答案】应助回帖

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daxiaobing: 金币+55, ★★★★★最佳答案, Thank you very much! 2017-12-15 10:50:20
This seems to be related to Jordan curve theorem, which is some kind of basis of ray casting algorithm that is used for detecting whether a point is inside or outside of a closed region.

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2楼2017-12-14 17:16:36
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daxiaobing

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引用回帖:
2楼: Originally posted by zaq123321 at 2017-12-14 17:16:36
This seems to be related to Jordan curve theorem, which is some kind of basis of ray casting algorithm that is used for detecting whether a point is inside or outside of a closed region.
...

I'm still confused about the condition of the theorem. For example, the inverse function in first quadrant separates the plane in two parts, obviously, a curve connect the two parts must intersect with the inverse function curve( not closed), so I want to ask if the condition can be lower: only require the two parts are open sets, and the curve connect the two parts are continuous?
3楼2017-12-15 11:28:57
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zaq123321

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Can you post the theorem and it's proof that you mentioned? I don't understand what do you mean lower condition. Those two parts are one part is bounded and the other part is unbounded

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4楼2017-12-15 17:00:17
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daxiaobing

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引用回帖:
4楼: Originally posted by zaq123321 at 2017-12-15 17:00:17
Can you post the theorem and it's proof that you mentioned? I don't understand what do you mean lower condition. Those two parts are one part is bounded and the other part is unbounded
...

A is an open set in R^n, A* is the closure of A, and B is the complementary set of A*, C is a curve satisfies: the intersection of C and A is not empty, the intersection of C and B is not empty. Then the intersection of C and the boundary of A is not empty? how to prove it? thank you!
5楼2017-12-15 21:06:03
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zaq123321

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I don't recognize of this kind of proof. You might want to find some standard proof from textbook.

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6楼2017-12-15 22:03:15
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daxiaobing

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6楼: Originally posted by zaq123321 at 2017-12-15 22:03:15
I don't recognize of this kind of proof. You might want to find some standard proof from textbook.

Thank you for taking so much time to answer my question,your answer helped me a lot.
7楼2017-12-15 22:49:10
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