move plot_pareto from aquatic_udp_bench crate into own crate

plot_pareto/src/main.rs

@@ -0,0 +1,54 @@
+use plotly::{Plot, Scatter, Layout};
+use plotly::common::Title;
+use plotly::layout::Axis;
+use rand::{thread_rng, rngs::SmallRng, SeedableRng, Rng};
+use rand_distr::Pareto;
+
+
+fn main(){
+    let mut plot = Plot::new();
+    let mut rng = SmallRng::from_rng(thread_rng()).unwrap();
+
+    const LEN: usize = 1_000;
+    const MAX_VAL: usize = LEN - 1;
+
+    for pareto_shape in [0.1, 0.2, 0.3, 0.4, 0.5].iter() {
+        let pareto = Pareto::new(1.0, *pareto_shape).unwrap();
+
+        let mut y_axis = [0; LEN];
+
+        for _ in 1..1_000_000 {
+            let index = pareto_usize(&mut rng, pareto, MAX_VAL);
+
+            y_axis[index] += 1;
+        }
+
+        let x_axis: Vec<usize> = (0..MAX_VAL).into_iter().collect();
+
+        let trace = Scatter::new(x_axis, y_axis.to_vec())
+            .name(&format!("pareto shape = {}", pareto_shape));
+
+        plot.add_trace(trace);
+    }
+
+    let layout = Layout::new()
+        .title(Title::new("Pareto distribution"))
+        .xaxis(Axis::new().title(Title::new("Info hash index")))
+        .yaxis(Axis::new().title(Title::new("Num requests")));
+    
+    plot.set_layout(layout);
+
+    plot.show();
+}
+
+
+pub fn pareto_usize(
+    rng: &mut impl Rng,
+    pareto: Pareto<f64>,
+    max: usize,
+) -> usize {
+    let p: f64 = rng.sample(pareto);
+    let p = (p.min(101.0f64) - 1.0) / 100.0;
+
+    (p * max as f64) as usize
+}