From fa9b3145f9eedef1df73b6a8ba4b1fb2b706263f Mon Sep 17 00:00:00 2001
From: Pascal Serrarens <pascal@passer.life>
Date: Wed, 1 Jul 2026 17:17:36 +0200
Subject: [PATCH] Backpropagation over cluster part 1

---
 Runtime/Scripts/Core/Cluster.cs | 45 ++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/Runtime/Scripts/Core/Cluster.cs b/Runtime/Scripts/Core/Cluster.cs
index 18726f0..7dcfafb 100644
--- a/Runtime/Scripts/Core/Cluster.cs
+++ b/Runtime/Scripts/Core/Cluster.cs
@@ -366,6 +366,49 @@ namespace NanoBrain {
                 thingClusters.Remove(thingId);
         }
 
+
+        public List<Neuron> GetAllInstances(Neuron nucleus) {
+            List<Neuron> allInstances = new();
+
+            int ix = -1;
+            //foreach (Nucleus myNucleus in this.nuclei) {
+            for (; ix < this.nuclei.Count; ix++) {
+                if (this.nuclei[ix] == nucleus)
+                    break;
+            }
+            if (ix == this.nuclei.Count)
+                return allInstances;
+
+            foreach (Cluster instance in this.instances) {
+                List<Nucleus> otherNuclei = instance.nuclei;
+                if (otherNuclei[ix] is Neuron otherNeuron)
+                    allInstances.Add(otherNeuron);
+            }
+            return allInstances;
+        }
+
+        public void Backpropagation(Func<Cluster, Vector3> Observer, Vector3 target, float learningRate) {
+            foreach (Nucleus nucleus in this.instances[0].nuclei) {
+                if (nucleus is not Neuron neuron)
+                    continue;
+
+                foreach (Synapse synapse in neuron.synapses) {
+                    List<Neuron> allSynapseNeurons = GetAllInstances(synapse.neuron);
+
+                    Vector3 dSSRdW = Vector3.zero;
+                    for (int clusterIx = 0; clusterIx < this.instances.Length; clusterIx++) {
+                        Cluster clusterInstance = this.instances[clusterIx];
+                        Neuron neuronInstance = allSynapseNeurons[clusterIx];
+
+                        // Simple case, without receivers...
+                        dSSRdW += (Vector3)(-2 * (Observer(clusterInstance) - target) * neuronInstance.activation);
+                    }
+                    synapse.weight += learningRate * dSSRdW.magnitude;
+                }
+            }
+
+        }
+
         #endregion ClusterArray
 
         /// <summary>
@@ -724,7 +767,7 @@ namespace NanoBrain {
             foreach (Nucleus nucleus in this.nuclei.ToArray()) {
                 if (nucleus is not Cluster cluster)
                     continue;
-                List<Nucleus> receivers =  cluster.CollectReceivers();
+                List<Nucleus> receivers = cluster.CollectReceivers();
                 Debug.Log($"cluster receiver count = {receivers.Count}");
                 if (receivers.Count == 0)
                     this.nuclei.Remove(nucleus);