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9.2 证明引理 9.2.
引理 9.2 若
P
θ(Z)=P(Z∣Y,θ),则
F(P
,θ)=logP(Y∣θ).
证明:
F(P
,θ)=EP
[logP(Y,Z∣θ)]+H(P
)=EP
[logP(Y,Z∣θ)]−EP
logP
(Z)=Z∑logP(Y,Z∣θ)P
θ(Z)−Z∑logP
(Z)P
(Z)=Z∑logP(Y,Z∣θ)P(Z∣Y,θ)−Z∑logP(Z∣Y,θ)P(Z∣Y,θ)=Z∑P(Z∣Y,θ)(logP(Y,Z∣θ)−logP(Z∣Y,θ))=Z∑P(Z∣Y,θ)logP(Z∣Y,θ)P(Y,Z∣θ)=Z∑P(Z∣Y,θ)logP(Y∣θ)=logP(Y∣θ)Z∑P(Z∣Y,θ)=logP(Y∣θ)⋅1=logP(Y∣θ)
证毕.