Joint Distributed Discrete Random Variables 假设两个变量 X,YX,YX,Y，Marginal Probability Distribution of XXX 定义为 P(X)=∑Y∈SYP(X,Y)\mathbb{P}(X)=\sum_{Y\in S_Y}\mathbb{P}(X,Y) P(X)=Y∈SY∑P(X,Y)