From 88114cc048e3d6c6c614c2438b82e663e8610ffd Mon Sep 17 00:00:00 2001
From: Pascal Serrarens <pascal@passer.life>
Date: Mon, 6 Jul 2026 11:38:33 +0200
Subject: [PATCH] Simplify weight training by using 1D in the right way

---
 Runtime/Scripts/Core/Neuron.cs | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/Runtime/Scripts/Core/Neuron.cs b/Runtime/Scripts/Core/Neuron.cs
index 646607c..c0dfc6b 100644
--- a/Runtime/Scripts/Core/Neuron.cs
+++ b/Runtime/Scripts/Core/Neuron.cs
@@ -668,7 +668,7 @@ namespace NanoBrain {
 
         public void BackPropagation1D(float derivative, float learningRate) {
             foreach (Synapse synapse in this.synapses)
-                synapse.BackPropagation(this, derivative, learningRate);            
+                synapse.BackPropagation(this, derivative, learningRate);
 
             // Bias
             if (this.trainable) {
@@ -689,7 +689,14 @@ namespace NanoBrain {
 
         public void BackPropagation3D(Vector3 derivative, float learningRate) {
             foreach (Synapse synapse in this.synapses)
-                synapse.BackPropagation(this, derivative, learningRate);            
+                // synapse.BackPropagation(this, derivative, learningRate);
+                // As the weight cannot change the direction of the derivative
+                // we can use the simpler, 1D backpropagation here
+                // But we still need to determine the sign of the derivative
+                if (Synapse.AreOpposed(derivative, synapse.neuron.activation))
+                    synapse.BackPropagation(this, -derivative.magnitude, learningRate);
+                else
+                    synapse.BackPropagation(this, derivative.magnitude, learningRate);
 
             // Bias
             if (this.trainable) {