The following distribution is related to both the Normal Distribution and to the
Gamma Distribution 8.4.3. Initially, consider a gamma distribution with probability function given by the formula
\begin{equation*}
y = \frac{x^{r-1} \cdot e^{-x / \mu}}{\Gamma(r) \cdot \mu^r}.
\end{equation*}
Replacing \(\mu = 2\) and r with r/2 gives the special case
\begin{equation*}
y = \frac{x^{r/2-1} \cdot e^{-x/2}}{\Gamma(r/2) \cdot 2^{r/2}}
\end{equation*}
which is given a special name below.