Merge branch 'features/distribution' into dev

Author: Axect

examples/dist.rs

@@ -63,4 +63,18 @@ fn example() {
     println!("PDF at x = mean: {}", g.pdf(0.666666));
     println!("PDF at x = mode: {}", g.pdf(0.5));
     println!("");
+
+    let m = 1.0;
+    let s = 1.0;
+    let lognorm = LogNormal(m, s);
+    let lognorm_sample = lognorm.sample(SAMPLE_SIZE);
+    println!("LogNormal at (m,s) = ({},{})", m, s);
+    println!("Number of samples: {}", SAMPLE_SIZE);
+    println!("Theoretical mean: {}", lognorm.mean());
+    println!("Sample mean: {}", lognorm_sample.mean());
+    println!("Theoretical var: {}", lognorm.var());
+    println!("Sample var: {}", lognorm_sample.var());
+    println!("PDF at x = mean: {}", lognorm.pdf(2.718281828459045));
+    println!("PDF at x = mode: {}", lognorm.pdf(1.0));
+    println!("");
 }

src/statistics/dist.rs

@@ -698,7 +698,7 @@ impl<T: PartialOrd + SampleUniform + Copy + Into<f64>> RNG for TPDist<T> {
             //            }
             Gamma(shape, scale) => {
                 let gamma =
-                    rand_distr::Gamma::<f64>::new((*shape).into(), (*scale).into()).unwrap();
+                    rand_distr::Gamma::<f64>::new((*shape).into(), 1f64 / (*scale).into()).unwrap();
                 gamma.sample_iter(rng).take(n).collect()
             } //            Gamma(a, b) => {
               //                let a_f64 = (*a).into();