diff -r f248e1434c3b -r df9628092285 src/zero.rs
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/zero.rs	Mon Oct 21 08:44:23 2024 -0500
@@ -0,0 +1,50 @@
+
+use alg_tools::mapping::Apply;
+use crate::manifold::ManifoldPoint;
+use crate::fb::{Grad, Desc, Prox};
+use std::marker::PhantomData;
+
+/// Zero function on manifolds.
+pub struct ZeroFn<M : ManifoldPoint> {
+    _phantoms : PhantomData<M>
+}
+
+impl<M: ManifoldPoint> ZeroFn<M> {
+    pub fn new() -> Self {
+        ZeroFn{_phantoms : PhantomData }
+    }
+}
+
+impl<M : ManifoldPoint> Apply<M> for ZeroFn<M> {
+    type Output = f64;
+
+    fn apply(&self, _x : M) -> Self::Output {
+        0.0
+    }
+}
+
+impl<'a, M : ManifoldPoint> Apply<&'a M> for ZeroFn<M> {
+    type Output = f64;
+
+    fn apply(&self, _x : &'a M) -> Self::Output {
+        0.0
+    }
+}
+
+impl<M : ManifoldPoint> Desc<M> for ZeroFn<M> {
+    fn desc(&self, _τ : f64, x : M) -> M {
+        x
+    }
+}
+
+impl<M : ManifoldPoint> Grad<M> for ZeroFn<M> {
+    fn grad(&self, x : &M) -> M::Tangent {
+       x.tangent_origin()
+    }
+}
+
+impl<M : ManifoldPoint> Prox<M> for ZeroFn<M> {
+    fn prox(&self, _τ : f64, x : M) -> M {
+        x
+    }
+}
\ No newline at end of file