Joint Entropy

Definition

Let $X$ and $Y$ be two discrete random variables taking values in $A_X$ and respectively.

The joint entropy is defined as:

$$H(X,Y)=\mathbb{E}\left[{\log }_2\frac{1}{p(X,Y)}\right]=\sum p(x,y){\log }_2\frac{1}{p(x,y)}[\text{bits}]$$