From 10e1dd01269e2097e5077d4a8d4ba8ac009b6417 Mon Sep 17 00:00:00 2001
From: Pascal Serrarens <pascal@passer.life>
Date: Mon, 6 Jul 2026 11:22:23 +0200
Subject: [PATCH] 3D DeltaWeight fix

---
 Runtime/Scripts/Core/Synapse.cs | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/Runtime/Scripts/Core/Synapse.cs b/Runtime/Scripts/Core/Synapse.cs
index 640cf04..9116e12 100644
--- a/Runtime/Scripts/Core/Synapse.cs
+++ b/Runtime/Scripts/Core/Synapse.cs
@@ -36,9 +36,7 @@ namespace NanoBrain {
             this.weight = weight;
         }
 
-        public virtual void BackPropagation(Neuron receiver, float error, float learningRate) {
-            float derivative = error;
-
+        public virtual void BackPropagation(Neuron receiver, float derivative, float learningRate) {
             switch (receiver.activator) {
                 case Neuron.ActivationType.Linear:
                     derivative *= 1;
@@ -67,8 +65,6 @@ namespace NanoBrain {
         }
 
         public virtual void BackPropagation(Neuron receiver, Vector3 derivative, float learningRate) {
-            //Vector3 derivative = error;
-
             switch (receiver.activator) {
                 case Neuron.ActivationType.Linear:
                     derivative *= 1;
@@ -83,21 +79,28 @@ namespace NanoBrain {
                     break;
                 default:
                     Debug.Log("other activator");
-                    break;               
+                    break;
             }
 
             this.neuron.BackPropagation3D(derivative * this.weight, learningRate);
 
-            derivative = Vector3.Scale(derivative, this.neuron.activation);
+            derivative *= math.length(this.neuron.activation);
 
             if (this.trainable) {
-                // Compared to the 1D solution, this does not decrease the weight.
-                // direction and sign are different....
-                // Perhaps the sign is determine by the direction of the derivative and the neuron activation?
-                // When they are oppositie, the sign is negative? (or the other way round...)
-                this.weight += learningRate * derivative.magnitude;
+                float deltaWeight = learningRate * derivative.magnitude;
+                // Compared to the 1D solution, this does not decrease the weight because magnitude is always positive
+                // derivative.direction and derivative.sign are different....
+                if (AreOpposed(derivative, this.neuron.activation))
+                    this.weight -= deltaWeight;
+                else
+                    this.weight += deltaWeight;
             }
         }
+
+        public static bool AreOpposed(Vector3 a, Vector3 b) {
+            // Check if the angle between the vectors is > 90 degrees
+            return Vector3.Dot(a, b) < 0f;
+        }
     }
 
 }
\ No newline at end of file