- E. Xing, S. Y. Cheng, Congwen Lu. 2015. Probabilistic Graphical Models , Spring 2015 2 : Directed GMs : Bayesian Networks. Abstract: Random variables and values: Random variables are denoted by upper-case letters, such as A,B,C and the value of random variables are denoted by lower-case letters, such as P (A = a|B = b, C = c), and here a, b, c are realizations for A,B,C. Random vectors: Random vectors are also denoted by upper-case letters, but they are vectors, for example: X = X1 X2 X3 , sometimes, it’s also denoted as − X . Here the subscript means the dimension of the random vector. For example X1 is the first dimension of X.
