I have two discrete random variables $X$ and $Y$, let $P_X$ and $P_Y$ be the PMF of the random variables, if $Y=X^2$ ,I want to know the PMF of Y in terms of PMF of X ?
I know how to do it with continuous RVs
$P_Y(y)=((P_X(sqrt(y))+P_X(-sqrt(y)))/(2*sqrt(y))$
is there a difference if X and Y are discrete RVs?