diff -r 99ad55974e62 -r 981069ef919b src/direct_product.rs
--- a/src/direct_product.rs	Mon Dec 30 15:46:28 2024 -0500
+++ b/src/direct_product.rs	Tue Dec 31 10:51:32 2024 -0500
@@ -287,6 +287,11 @@
 
     type Owned = Pair<A::Owned, B::Owned>;
 
+    fn add_mul<I : Instance<Pair<U,V>>>(self, α : F, x : I, β : F) -> Self::Owned {
+        let Pair(u, v) = x.decompose();
+        Pair(self.0.add_mul(α, u, β), self.1.add_mul(α, v, β))
+    }
+
     fn axpy<I : Instance<Pair<U,V>>>(&mut self, α : F, x : I, β : F) {
         let Pair(u, v) = x.decompose();
         self.0.axpy(α, u, β);