From 2777d4f6daf48d7c8be0696251397194c9f05a0d Mon Sep 17 00:00:00 2001
From: Cedric <cedric00ik@gmail.com>
Date: Tue, 28 Apr 2026 06:46:26 +0000
Subject: [PATCH] feat: adjacency builder

---
 .../trainers/PPOTrainer.py                    | 83 ++++++++++++++++---
 tests/test_adjacency.py                       | 79 ++++++++++++++++++
 2 files changed, 149 insertions(+), 13 deletions(-)
 create mode 100644 tests/test_adjacency.py

diff --git a/src/brittle_star_project/trainers/PPOTrainer.py b/src/brittle_star_project/trainers/PPOTrainer.py
index df2c571..2642446 100644
--- a/src/brittle_star_project/trainers/PPOTrainer.py
+++ b/src/brittle_star_project/trainers/PPOTrainer.py
@@ -27,10 +27,11 @@ from brittle_star_project.ppo import PPO
 from enum import Enum
 
 
-class ObsMode(Enum):
-    CENTRALIZED = "centralized"
-    ARM = "arm"
-    SEGMENT = "segment"
+class MorphMode(Enum):
+    CENTRALIZED = 0
+    FULLY_CONNECTED = 1
+    RING = 2
+    SEGMENT = 3
 
 
 # TODO: move to config
@@ -49,6 +50,71 @@ _ALLOWED_OBS_KEYS = {
 # TODO: clip scaled reward?
 
 
+def build_adjacency(segments_per_arm, mode: MorphMode):
+    num_arms = len(segments_per_arm)
+    num_segments = sum(segments_per_arm)
+
+    # FOR NOW SEMI HARDCODE:
+    # CENTRALIZED: 1 agent, no stress, adja = 1,1 = [[1]]
+    # FULLY CONNECTED: 5 agents: adj = alle 1
+    # CENTRAL DISK:#arms= 5 agents, only neighbor as adjacent so diagonal kinda..
+    # ARM = #segments agents: diago kinda, but extra, center ring too, put center mlps first or..
+
+    if mode == MorphMode.CENTRALIZED:
+        return jnp.ones((1, 1))
+
+    if mode == MorphMode.FULLY_CONNECTED:
+        adj = jnp.ones((num_arms, num_arms))  # everybody adjacent everybody
+        return adj
+
+    if mode == MorphMode.RING:  # ring
+        adj = jnp.zeros((num_arms, num_arms))
+        for i in range(num_arms):
+            adj = adj.at[i, i].set(1)  # self
+            adj = adj.at[i, (i - 1) % num_arms].set(1)
+            adj = adj.at[i, (i + 1) % num_arms].set(1)  # left and right..
+        return adj
+
+    if mode == MorphMode.SEGMENT:
+        num_nodes = num_arms + num_segments
+        adj = jnp.zeros((num_nodes, num_nodes))
+
+        # first ring
+        for i in range(num_arms):
+            # self
+            adj = adj.at[i, i].set(1)
+
+            # ring neighbors
+            adj = adj.at[i, (i - 1) % num_arms].set(1)
+            adj = adj.at[i, (i + 1) % num_arms].set(1)
+
+        # then segment chains
+        idx = 0
+        for arm_idx, seg_count in enumerate(segments_per_arm):
+            for i in range(seg_count):
+                seg_node = num_arms + idx + i
+
+                adj = adj.at[seg_node, seg_node].set(1)
+                if i > 0:
+                    adj = adj.at[seg_node, seg_node - 1].set(1)
+                if i < seg_count - 1:
+                    adj = adj.at[seg_node, seg_node + 1].set(1)
+
+            idx += seg_count
+
+        idx = 0
+        for arm_idx, seg_count in enumerate(segments_per_arm):
+            first_seg = num_arms + idx  # first segment of this arm
+
+            # connect ring node first segment
+            adj = adj.at[arm_idx, first_seg].set(1)
+            adj = adj.at[first_seg, arm_idx].set(1)
+
+            idx += seg_count
+
+        return adj
+
+
 @jax.jit
 def _clip_action(action: jnp.ndarray, low: jnp.ndarray, high: jnp.ndarray) -> jnp.ndarray:
     return jnp.clip(action, low, high)
@@ -71,15 +137,6 @@ def _normalize_obs(obs, mean, var, eps=1e-8):
     return jnp.clip((obs - mean) / jnp.sqrt(var + eps), -10.0, 10.0)
 
 
-from enum import Enum
-
-
-class ObsMode(Enum):
-    CENTRALIZED = 0
-    ARM = 1
-    SEGMENT = 2
-
-
 @jax.jit
 def _convert_obs_dict_to_array(obs_dict, obs_mode, segments_per_arm):
 
diff --git a/tests/test_adjacency.py b/tests/test_adjacency.py
new file mode 100644
index 0000000..5c33038
--- /dev/null
+++ b/tests/test_adjacency.py
@@ -0,0 +1,79 @@
+import jax.numpy as jnp
+import pytest
+
+from brittle_star_project.trainers.PPOTrainer import build_adjacency, MorphMode
+
+
+def assert_symmetric(adj):
+    assert jnp.all(adj == adj.T)
+
+
+def test_centralized():
+    adj = build_adjacency([4, 4, 4, 4, 4], MorphMode.CENTRALIZED)
+
+    assert adj.shape == (1, 1)
+    assert adj[0, 0] == 1
+
+
+def test_fully_connected():
+    adj = build_adjacency([4, 4, 4, 4, 4], MorphMode.FULLY_CONNECTED)
+
+    assert adj.shape == (5, 5)
+    assert jnp.all(adj == 1)
+
+
+def test_ring():
+    adj = build_adjacency([4, 4, 4, 4, 4], MorphMode.RING)
+
+    assert adj.shape == (5, 5)
+    assert_symmetric(adj)
+
+    # each node should connect to itself + 2 neighbors
+    for i in range(5):
+        assert adj[i, i] == 1
+        assert jnp.sum(adj[i]) == 3
+
+
+def test_segment_structure():
+    segments = [4, 4, 4, 4, 4]
+    adj = build_adjacency(segments, MorphMode.SEGMENT)
+
+    num_arms = 5
+    num_segments = sum(segments)
+    num_nodes = num_arms + num_segments
+
+    assert adj.shape == (num_nodes, num_nodes)
+
+    # --- ring connectivity ---
+    for i in range(num_arms):
+        assert adj[i, i] == 1
+        assert adj[i, (i - 1) % num_arms] == 1
+        assert adj[i, (i + 1) % num_arms] == 1
+
+    # --- segment chain checks ---
+    offset = num_arms
+    for arm in range(5):
+        for i in range(4):
+            node = offset + arm * 4 + i
+
+            # self
+            assert adj[node, node] == 1
+
+            # chain neighbors
+            if i > 0:
+                assert adj[node, node - 1] == 1
+            if i < 3:
+                assert adj[node, node + 1] == 1
+
+    # --- ring ↔ segment connections ---
+    for arm in range(5):
+        first_seg = num_arms + arm * 4
+        assert adj[arm, first_seg] == 1
+        assert adj[first_seg, arm] == 1
+
+
+def test_no_isolated_nodes():
+    adj = build_adjacency([4, 4, 4, 4, 4], MorphMode.SEGMENT)
+
+    # no node should be completely isolated
+    assert jnp.all(jnp.sum(adj, axis=0) > 0)