diff -r 99ad55974e62 -r d5b0e496b72f src/operator_arithmetic.rs
--- a/src/operator_arithmetic.rs	Mon Dec 30 15:46:28 2024 -0500
+++ b/src/operator_arithmetic.rs	Mon Jan 06 20:29:25 2025 -0500
@@ -2,7 +2,7 @@
 Arithmetic of [`Mapping`]s.
  */
 
-use serde::Serialize;
+use serde::{Serialize, Deserialize};
 use crate::types::*;
 use crate::instance::{Space, Instance};
 use crate::mapping::{Mapping, DifferentiableImpl, DifferentiableMapping};
@@ -22,7 +22,7 @@
 }
 
 /// Weighting of a [`Mapping`] by scalar multiplication.
-#[derive(Copy,Clone,Debug,Serialize)]
+#[derive(Copy,Clone,Debug,Serialize,Deserialize)]
 pub struct Weighted<T, C : Constant> {
     /// The weight
     pub weight : C,
@@ -73,7 +73,7 @@
 }
 
 /// A sum of [`Mapping`]s.
-#[derive(Serialize, Debug, Clone)]
+#[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct MappingSum<M>(Vec<M>);
 
 impl< M> MappingSum<M> {