Add a parallel version of the previous example

Cargo.toml

@@ -25,6 +25,7 @@ nightly = []
 criterion = "0.3.5"
 roots = "0.0.7"
 rand = "0.8.5"
+rayon = "1.8.0"
 
 [[example]]
 name = "basic"

examples/x_sinx_levels_par.rs

@@ -0,0 +1,29 @@
+//! Parallel version of `x_sinx_levels.rs`.
+
+use std::{error::Error, iter, time::Instant};
+use root1d::{bisect, toms748};
+use rand::prelude::*;
+use rayon::prelude::*;
+
+fn main() -> Result<(), Box<dyn Error + 'static>> {
+    const N: usize = 100_000;
+    let levels: Vec<_> = iter::from_fn(|| Some(1.5 * random::<f64>()))
+        .take(N).collect();
+    let mut out = vec![0.0; N];
+
+    let now = Instant::now();
+    levels
+        .par_iter()
+        .map(|lv| bisect(|x: f64| x * x.sin() - lv, 0., 2.).root().unwrap())
+        .collect_into_vec(&mut out);
+    println!("bisect: {} secs", now.elapsed().as_secs_f64());
+
+    let now = Instant::now();
+    levels
+        .par_iter()
+        .map(|lv| toms748(|x: f64| x * x.sin() - lv, 0., 2.).root().unwrap())
+        .collect_into_vec(&mut out);
+    println!("toms748: {} secs", now.elapsed().as_secs_f64());
+
+    Ok(())
+}