diff --git a/src/functions-reference/positive_continuous_distributions.Rmd b/src/functions-reference/positive_continuous_distributions.Rmd index 53cf2a813..d9c355aad 100644 --- a/src/functions-reference/positive_continuous_distributions.Rmd +++ b/src/functions-reference/positive_continuous_distributions.Rmd @@ -368,11 +368,13 @@ 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 $y \in \mathbb{R}^+$, \[ \text{Gamma}(y|\alpha,\beta) = \frac{\beta^{\alpha}} {\Gamma(\alpha)} \, y^{\alpha - 1} \exp(-\beta \, y) . \] +Under the shape and rate formulation of the Gamma distribution, $E(y) = \alpha/\beta$ and $\var(y) = \alpha/\beta^2$. + ### Sampling statement `y ~ ` **`gamma`**`(alpha, beta)` diff --git a/src/functions-reference/real-valued_basic_functions.Rmd b/src/functions-reference/real-valued_basic_functions.Rmd index 72aba24b6..b82570869 100644 --- a/src/functions-reference/real-valued_basic_functions.Rmd +++ b/src/functions-reference/real-valued_basic_functions.Rmd @@ -1217,7 +1217,7 @@ Return the natural logarithm of the beta function applied to alpha and beta. The beta function, $\text{B}(\alpha,\beta)$, computes the normalizing constant for the beta distribution, and is defined for $\alpha > 0$ and $\beta > 0$. \[ \text{lbeta}(\alpha,\beta) = \log -\Gamma(a) + \log \Gamma(b) - \log \Gamma(a+b) \] See section +\Gamma(\alpha) + \log \Gamma(\beta) - \log \Gamma(\alpha+\beta) \] See section [appendix](#beta-appendix) for definition of $\text{B}(\alpha, \beta)$. `r since("2.0")`