Max Entropy Model study note
2013-08-22 15:47
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随机事件的信息熵:设随机变量ξ,它有A1,A2,A3,A4,……,An共n种可能的结局,每个结局出现的概率分别为p1,p2,p3,p4,……,pn,则其不确定程度,即信息熵为:
举例:抛硬币
p(head) = 0.5, p(tail) = 0.5
信息熵为H(p) = -(0.5 * log(0.5) * 2) = -log0.5 = 1(log以2为底)
设最终输出值构成的语言学类别有限集为Y,对于每个y∈Y,其生成均受上下文信息x的影响和约束。已知与y有关的所有上下文信息组成的集合为X,则模型的目标是:给定上下文x∈X,计算输出为y∈Y的条件概率p(y|x)。
举例:抛硬币
p(head) = 0.5, p(tail) = 0.5
信息熵为H(p) = -(0.5 * log(0.5) * 2) = -log0.5 = 1(log以2为底)
设最终输出值构成的语言学类别有限集为Y,对于每个y∈Y,其生成均受上下文信息x的影响和约束。已知与y有关的所有上下文信息组成的集合为X,则模型的目标是:给定上下文x∈X,计算输出为y∈Y的条件概率p(y|x)。
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