Added project_on to InnerSpace

src/structure.rs

@@ -246,6 +246,15 @@ pub trait InnerSpace: VectorSpace where
     fn lerp(self, other: Self, amount: Self::Scalar) -> Self {
         self + ((other - self) * amount)
     }
+
+    /// Returns the
+    /// [vector projection](https://en.wikipedia.org/wiki/Vector_projection)
+    /// of the current inner space projected onto the supplied argument.
+    #[inline]
+    #[must_use]
+    fn project_on(self, other: Self) -> Self {
+        other * (self.dot(other) / other.magnitude2())
+    }
 }
 
 /// Points in a [Euclidean space](https://en.wikipedia.org/wiki/Euclidean_space)

tests/vector.rs

@@ -248,6 +248,13 @@ fn test_normalize() {
     assert_ulps_eq!(Vector4::new(1.0f64, 2.0f64, 4.0f64, 10.0f64).normalize(), &Vector4::new(1.0/11.0, 2.0/11.0, 4.0/11.0, 10.0/11.0));
 }
 
+#[test]
+fn test_project_on() {
+    assert_ulps_eq!(Vector2::new(-1.0f64, 5.0).project_on(Vector2::new(2.0, 4.0)), &Vector2::new(9.0/5.0, 18.0/5.0));
+    assert_ulps_eq!(Vector3::new(5.0f64, 6.0, 7.0).project_on(Vector3::new(1.0, 1.0, 1.0)), &Vector3::new(6.0, 6.0, 6.0));
+    assert_ulps_eq!(Vector4::new(0.0f64, -5.0, 5.0, 5.0).project_on(Vector4::new(0.0, 1.0, 0.0, 0.5)), &Vector4::new(0.0, -2.0, 0.0, -1.0));
+}
+
 #[test]
 fn test_cast() {
     assert_ulps_eq!(Vector2::new(0.9f64, 1.5).cast(), Vector2::new(0.9f32, 1.5));