diff -r e09437844ad9 -r f248e1434c3b src/dist.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/dist.rs	Sat Oct 19 10:46:13 2024 -0500
@@ -0,0 +1,60 @@
+
+use alg_tools::mapping::Apply;
+use crate::manifold::ManifoldPoint;
+use crate::fb::{Grad, Desc};
+
+/// Structure for distance-to functions
+pub struct DistTo<M : ManifoldPoint> {
+    base : M
+}
+
+impl<M : ManifoldPoint> Apply<M> for DistTo<M> {
+    type Output = f64;
+
+    fn apply(&self, x : M) -> Self::Output {
+        self.base.dist_to(&x)
+    }
+}
+
+impl<'a, M : ManifoldPoint> Apply<&'a M> for DistTo<M> {
+    type Output = f64;
+
+    fn apply(&self, x : &'a M) -> Self::Output {
+        self.base.dist_to(x)
+    }
+}
+
+/// Structure for distance-to functions
+pub struct DistToSquaredDiv2<M : ManifoldPoint> {
+    base : M
+}
+
+impl<M : ManifoldPoint> Apply<M> for DistToSquaredDiv2<M> {
+    type Output = f64;
+
+    fn apply(&self, x : M) -> Self::Output {
+        let d = self.base.dist_to(&x);
+        d*d / 2.0
+    }
+}
+
+impl<'a, M : ManifoldPoint> Apply<&'a M> for DistToSquaredDiv2<M> {
+    type Output = f64;
+
+    fn apply(&self, x : &'a M) -> Self::Output {
+        let d = self.base.dist_to(x);
+        d*d / 2.0
+    }
+}
+
+impl<M : ManifoldPoint> Desc<M> for DistToSquaredDiv2<M> {
+    fn desc(&self, τ : f64, x : M) -> M {
+        x.exp(&(self.grad(&x) * τ))
+    }
+}
+
+impl<M : ManifoldPoint> Grad<M> for DistToSquaredDiv2<M> {
+    fn grad(&self, x : &M) -> M::Tangent {
+       x.log(&self.base)
+    }
+}