Let X {\displaystyle X} and Y {\displaystyle Y} be modeled as random variables. Furthermore, let p Y | X ( y | x ) {\displaystyle p_{Y|X}(y|x)} be the conditional probability distribution function of Y {\displaystyle Y} given X {\displaystyle X} , which is an inherent fixed property of the communication channel. Then the choice of the marginal distribution p X ( x ) {\displaystyle p_{X}(x)} completely determines the joint distribution p X , Y ( x , y ) {\displaystyle p_{X,Y}(x,y)} due to the identity