Added information to ln_beta argument

src/beta.rs

@@ -16,6 +16,8 @@ pub trait Beta {
     /// [1]: http://people.sc.fsu.edu/~jburkardt/c_src/asa109/asa109.html
     /// [2]: http://www.jstor.org/stable/2346797
     /// [3]: http://www.jstor.org/stable/2346887
+    /// 
+    /// ln_beta should be precomputed as `p.ln_beta(q)`.
     fn inc_beta(self, p: Self, q: Self, ln_beta: Self) -> Self;
 
     /// Compute the inverse of the regularized incomplete beta function.
@@ -27,6 +29,8 @@ pub trait Beta {
     /// [1]: http://people.sc.fsu.edu/~jburkardt/c_src/asa109/asa109.html
     /// [2]: http://www.jstor.org/stable/2346798
     /// [3]: http://www.jstor.org/stable/2346887
+    /// 
+    /// ln_beta should be precomputed as `p.ln_beta(q)`.
     fn inv_inc_beta(self, p: Self, q: Self, ln_beta: Self) -> Self;
 
     /// Compute the natural logarithm of the beta function.