Add a multi optimizer (#1916)

python/tests/test_tree.py

@@ -3,6 +3,7 @@
 import unittest
 
 import mlx.core as mx
+import mlx.nn as nn
 import mlx.utils
 import mlx_tests
 
@@ -22,6 +23,29 @@ class TestTreeUtils(mlx_tests.MLXTestCase):
         self.assertEqual(list(zip(*flat_tree))[1], vals)
         self.assertEqual(mlx.utils.tree_unflatten(flat_tree), tree)
 
+    def test_merge(self):
+        t1 = {"a": 0}
+        t2 = {"b": 1}
+        t = mlx.utils.tree_merge(t1, t2)
+        self.assertEqual({"a": 0, "b": 1}, t)
+        with self.assertRaises(ValueError):
+            mlx.utils.tree_merge(t1, t1)
+        with self.assertRaises(ValueError):
+            mlx.utils.tree_merge(t, t1)
+
+        mod1 = nn.Sequential(nn.Linear(2, 2), nn.Linear(2, 2))
+        mod2 = nn.Sequential(nn.Linear(2, 2), nn.Linear(2, 2))
+        mod = nn.Sequential(mod1, mod2)
+
+        params1 = {"layers": [mod1.parameters()]}
+        params2 = {"layers": [None, mod2.parameters()]}
+        params = mlx.utils.tree_merge(params1, params2)
+        for (k1, v1), (k2, v2) in zip(
+            mlx.utils.tree_flatten(params), mlx.utils.tree_flatten(mod.parameters())
+        ):
+            self.assertEqual(k1, k2)
+            self.assertTrue(mx.array_equal(v1, v2))
+
 
 if __name__ == "__main__":
     unittest.main()