# HG changeset patch
# User Tuomo Valkonen <tuomov@iki.fi>
# Date 1729518263 18000
# Node ID df962809228557f0290517dcec415f6e4d56e97c
# Parent  f248e1434c3bfb6fa15834b6fee5dcc876257354
Add a zero function on manifolds

diff -r f248e1434c3b -r df9628092285 src/cube.rs
--- a/src/cube.rs	Sat Oct 19 10:46:13 2024 -0500
+++ b/src/cube.rs	Mon Oct 21 08:44:23 2024 -0500
@@ -232,6 +232,10 @@
     fn dist_to(&self, other : &Self) -> f64 {
         self.log_dist(other).1
     }
+
+    fn tangent_origin(&self) -> Self::Tangent {
+        Loc([0.0, 0.0])
+    }
 }
 
 #[cfg(test)]
diff -r f248e1434c3b -r df9628092285 src/main.rs
--- a/src/main.rs	Sat Oct 19 10:46:13 2024 -0500
+++ b/src/main.rs	Mon Oct 21 08:44:23 2024 -0500
@@ -9,6 +9,7 @@
 mod fb;
 mod cube;
 mod dist;
+mod zero;
 
 fn main() {
 
diff -r f248e1434c3b -r df9628092285 src/manifold.rs
--- a/src/manifold.rs	Sat Oct 19 10:46:13 2024 -0500
+++ b/src/manifold.rs	Mon Oct 21 08:44:23 2024 -0500
@@ -14,5 +14,8 @@
 
     /// Distance to `other`
     fn dist_to(&self, other : &Self) -> f64;
+
+    /// Return the zero tangent at `self`.
+    fn tangent_origin(&self) -> Self::Tangent;
 }
 
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
+    }
+}
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