From 1f813379130d29d4713c7f3767f43255a31d5a07 Mon Sep 17 00:00:00 2001
From: Alain Zscheile <fogti+devel@ytrizja.de>
Date: Fri, 5 Jan 2024 20:46:14 +0100
Subject: [PATCH] +dumbbell

---
 src/ex.rs  | 8 ++++++++
 src/lib.rs | 5 +++++
 2 files changed, 13 insertions(+)

diff --git a/src/ex.rs b/src/ex.rs
index 6f30f94..e9eb823 100644
--- a/src/ex.rs
+++ b/src/ex.rs
@@ -34,6 +34,14 @@ pub fn circle_sin_chain1(w: f64) -> impl Fn(f64) -> [f64; 2] {
     }
 }
 
+// source: https://mathworld.wolfram.com/DumbbellCurve.html
+pub fn dumbbell(a: f64) -> impl Fn(f64) -> [f64; 2] {
+    move |t: f64| {
+        let t2 = t * t;
+        [a * t, a * t2 * (1.0 - t2).sqrt()]
+    }
+}
+
 pub fn ellipse(a: f64, b: f64) -> impl Fn(f64) -> [f64; 2] {
     move |t: f64| {
         let cdat = circle(t);
diff --git a/src/lib.rs b/src/lib.rs
index 0f515b0..cc166ab 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -12,6 +12,7 @@ pub enum SelectExample {
     CassiniAntiAstroid { ca: f64, cc: f64, aa: f64 },
     CassiniAstroidTsq { ca: f64, cc: f64, aa: f64 },
 
+    Dumbbell { a: f64 },
     Ellipse { a: f64, b: f64 },
     Lemniskate { a: f64 },
     CirclePow { k: f64 },
@@ -42,6 +43,9 @@ impl SelectExample {
                 *cc += l;
                 *aa += l;
             }
+            Self::Dumbbell { a } => {
+                *a += l;
+            }
             Self::Ellipse { a, b } => {
                 *a /= 1.0 + l;
                 *b *= 1.0 + l;
@@ -79,6 +83,7 @@ impl SelectExample {
                 let x = ex::cassini_astroid(ca, cc, aa);
                 Box::new(move |t: f64| x(t * t))
             }
+            Self::Dumbbell { a } => Box::new(ex::dumbbell(a)),
             Self::Ellipse { a, b } => Box::new(ex::ellipse(a, b)),
             Self::Lemniskate { a } => Box::new(move |t: f64| ex::lemniskate(t, a)),
             Self::CirclePow { k } => Box::new(ex::circle_pow(k)),