DOC: update inverse CDF docstrings

src/distribution/chi_squared.rs

@@ -145,7 +145,7 @@ impl ContinuousCDF<f64, f64> for ChiSquared {
     /// # Formula
     ///
     /// ```text
-    /// (1 / Γ(k / 2)) * γ(k / 2, x / 2)
+    /// γ^{-1}(k / 2, x * Γ(k / 2) / 2)
     /// ```
     ///
     /// where `k` is the degrees of freedom, `Γ` is the gamma function,

src/distribution/erlang.rs

@@ -123,6 +123,17 @@ impl ContinuousCDF<f64, f64> for Erlang {
         self.g.sf(x)
     }
 
+    /// Calculates the inverse cumulative distribution function for the erlang
+    /// distribution at `x`
+    ///
+    /// # Formula
+    ///
+    /// ```text
+    /// γ^{-1}(k, (k - 1)! x) / λ
+    /// ```
+    ///
+    /// where `k` is the shape, `λ` is the rate, and `γ` is the upper
+    /// incomplete gamma function
     fn inverse_cdf(&self, p: f64) -> f64 {
         self.g.inverse_cdf(p)
     }

src/distribution/fisher_snedecor.rs

@@ -162,7 +162,8 @@ impl ContinuousCDF<f64, f64> for FisherSnedecor {
     /// # Formula
     ///
     /// ```text
-    /// I_((d1 * x) / (d1 * x + d2))(d1 / 2, d2 / 2)
+    /// z = I^{-1}_(x)(d1 / 2, d2 / 2)
+    /// d2 / (d1 (1 / z - 1))
     /// ```
     ///
     /// where `d1` is the first degree of freedom, `d2` is

src/distribution/triangular.rs

@@ -145,7 +145,7 @@ impl ContinuousCDF<f64, f64> for Triangular {
     /// if x < (mode - min) / (max - min) {
     ///     min + ((max - min) * (mode - min) * x)^(1 / 2)
     /// } else {
-    ///     max - (1 - (max - min) * (max - mode) * x)^(1 / 2)
+    ///     max - ((max - min) * (max - mode) * (1 - x))^(1 / 2)
     /// }
     /// ```
     fn inverse_cdf(&self, p: f64) -> f64 {
@@ -157,9 +157,9 @@ impl ContinuousCDF<f64, f64> for Triangular {
         }
 
         if p < (c - a) / (b - a) {
-            a + ((c - a) * (b - a) * p).powf(0.5)
+            a + ((c - a) * (b - a) * p).sqrt()
         } else {
-            b - ((b - a) * (b - c) * (1.0 - p)).powf(0.5)
+            b - ((b - a) * (b - c) * (1.0 - p)).sqrt()
         }
     }
 }