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@ -8,3 +8,68 @@ Knowledge tree
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> P(y|x),P给定x的条件下,y的概率。如:P(y=我招女孩子喜欢的概率|我是学生)
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> P(y|x),P给定x的条件下,y的概率。如:P(y=我招女孩子喜欢的概率|我是学生)
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### 一个小故事
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A story
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1. 女朋友和妈妈掉河里,路人拿出3颗豆,两颗红豆1颗绿豆。如果我抽中红豆救女朋友,抽中绿豆救妈妈。
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2. 我和路人各种抽一颗,路人发现自己抽中的是绿豆,他想用剩下的那颗跟我换,我换不换?换豆和女朋友活下去的概率一样吗?
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**直觉来讲**:
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换不换豆我抽中红豆的概率应该都是1/3。这时路人跟我说他的是绿豆,排除一颗,我抽中红豆的概率是1/2。换不换概率都是1/2
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**条件概率**:
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P(A|B)表示在B发生的条件下,发生A的概率。
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计算:设A表示我抽中的是红豆,B表示路人抽中的是绿豆
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结论:如果要救女朋友,最好和路人交换(2/3)。如果要救妈,最好不要换。
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### 直观理解
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Intuitive understanding
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假设有一个手写数据集,里面有100条记录,分别是0-10。
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此时小红写了个数字X,怎么判断是数字几?
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朴素贝叶斯工作原理:
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P(Y = 0|X) = ?, P(Y = 1|X)=? ......, P(Y = 10|X) = ?
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找到概率最高的,就是对应的数字。
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### 数学理解
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Mathmetical
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上面的数字判别公式修改为P(Y=Ck|X=x)。
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