diff --git a/src/functions-reference/positive_continuous_distributions.qmd b/src/functions-reference/positive_continuous_distributions.qmd index aa2b05cd2..5f3761809 100644 --- a/src/functions-reference/positive_continuous_distributions.qmd +++ b/src/functions-reference/positive_continuous_distributions.qmd @@ -360,11 +360,13 @@ For a description of argument and return types, see section ### Probability density function -If $\alpha \in \mathbb{R}^+$ and $\beta \in \mathbb{R}^+$, then for $y +If the shape parameter $\alpha \in \mathbb{R}^+$ and the rate (or inverse scale) parameter $\beta \in \mathbb{R}^+$, then for $y \in \mathbb{R}^+$, \begin{equation*} \text{Gamma}(y|\alpha,\beta) = \frac{\beta^{\alpha}} {\Gamma(\alpha)} \, y^{\alpha - 1} \exp(-\beta \, y) . \end{equation*} +Under the shape and rate formulation of the Gamma distribution, $\mathbb{E}[y] = \alpha / \beta$ and $\textrm{var}[y] = \alpha / \beta^2$. + ### Distribution statement `y ~ ` **`gamma`**`(alpha, beta)` diff --git a/src/functions-reference/real-valued_basic_functions.qmd b/src/functions-reference/real-valued_basic_functions.qmd index 9bf3fd8a9..2ce19f6cc 100644 --- a/src/functions-reference/real-valued_basic_functions.qmd +++ b/src/functions-reference/real-valued_basic_functions.qmd @@ -1193,7 +1193,7 @@ beta. The beta function, $\text{B}(\alpha,\beta)$, computes the normalizing constant for the beta distribution, and is defined for $\alpha > 0$ and $\beta > 0$. \begin{equation*} -\text{lbeta}(\alpha,\beta) = \log \Gamma(a) + \log \Gamma(b) - \log \Gamma(a+b) +\text{lbeta}(\alpha,\beta) = \log \Gamma(\alpha) + \log \Gamma(\beta) - \log \Gamma(\alpha+\beta) \end{equation*} See section [appendix](mathematical_functions.qmd#beta-appendix) for definition of $\text{B}(\alpha, \beta)$. {{< since 2.0 >}}