Independent wd for orthogonalized optimizer (#66)

* added independent wd

Signed-off-by: mikail <mkhona@nvidia.com>

Author: mkhona-nvidia

emerging_optimizers/orthogonalized_optimizers/muon.py

@@ -66,7 +66,8 @@ def __init__(
         momentum_beta: float = 0.95,
         use_nesterov: bool = False,
         weight_decay: float = 0.01,
-        use_decoupled_weight_decay: bool = True,
+        use_decoupled_wd: bool = True,
+        use_independent_wd: bool = False,
         fp32_matmul_prec: str = "medium",
         coefficient_type: str = "quintic",
         num_ns_steps: int = 5,
@@ -106,7 +107,8 @@ def scaled_orthogonalize_fn(grad: torch.Tensor) -> torch.Tensor:
             momentum_beta,
             use_nesterov,
             weight_decay,
-            use_decoupled_weight_decay,
+            use_decoupled_wd,
+            use_independent_wd,
             fp32_matmul_prec,
             scaled_orthogonalize_fn,
         )

emerging_optimizers/orthogonalized_optimizers/orthogonalized_optimizer.py

@@ -35,7 +35,9 @@
         use_nesterov: Whether to use Nesterov-style momentum in the internal SGD.
         weight_decay: The weight decay used by the optimizer, default to be decoupled weight decay.
             See Decoupled Weight Decay Regularization: https://arxiv.org/abs/1711.05101
-        use_decoupled_weight_decay: Whether to use decoupled weight decay, default to be True.
+        use_decoupled_wd: Whether to use decoupled weight decay, default to be True.
+        use_independent_wd: Whether to use independent weight decay (https://arxiv.org/abs/2510.19093),
+            default to be False.
         fp32_matmul_prec: Precision of the matmul operations in optimizer states GEMM operations.
 """
 
@@ -99,7 +101,8 @@ def __init__(
         momentum_beta: float,
         use_nesterov: bool,
         weight_decay: float,
-        use_decoupled_weight_decay: bool,
+        use_decoupled_wd: bool,
+        use_independent_wd: bool,
         fp32_matmul_prec: str,
         scaled_orthogonalize_fn: Callable | None = None,
         **kwargs: Any,
@@ -114,7 +117,8 @@ def __init__(
             momentum_beta=momentum_beta,
             use_nesterov=use_nesterov,
             weight_decay=weight_decay,
-            use_decoupled_weight_decay=use_decoupled_weight_decay,
+            use_decoupled_wd=use_decoupled_wd,
+            use_independent_wd=use_independent_wd,
             **kwargs,
         )
 
@@ -152,9 +156,14 @@ def step(self, closure: Callable[[], float] | None = None) -> float | None:
 
                 # Apply weight decay
                 if group["weight_decay"] > 0.0:
-                    if group["use_decoupled_weight_decay"]:
-                        # Apply decoupled weight decay
-                        p.add_(p, alpha=(-group["lr"] * group["weight_decay"]))
+                    if group["use_decoupled_wd"]:
+                        # Apply weight decay directly to params without changing gradients
+                        if group["use_independent_wd"]:
+                            # do not tie weight decay and learning rate
+                            weight_decay_scale = group["weight_decay"]
+                        else:
+                            weight_decay_scale = group["weight_decay"] * group["lr"]
+                        p.add_(p, alpha=(-weight_decay_scale))
                     else:
                         # add l2 regularization before preconditioning (i.e. adding a squared loss term)
                         grad += group["weight_decay"] * p

tests/test_orthogonalized_optimizer.py

@@ -42,7 +42,8 @@ def test_orthogonalized_optimizer_core_matches_sgd(self, shape) -> None:
             momentum_beta=0,
             use_nesterov=False,
             weight_decay=0.5,
-            use_decoupled_weight_decay=True,
+            use_decoupled_wd=True,
+            use_independent_wd=False,
             fp32_matmul_prec="highest",
         )
 
@@ -83,7 +84,8 @@ def test_orthogonalized_optimizer_core_matches_sgd_with_momentum(self, shape) ->
             momentum_beta=0.5,
             use_nesterov=False,
             weight_decay=0.0,
-            use_decoupled_weight_decay=False,
+            use_decoupled_wd=False,
+            use_independent_wd=False,
             fp32_matmul_prec="highest",
         )
 
@@ -133,7 +135,8 @@ def dummy_interleaved_split_orth_fn(x: torch.Tensor) -> torch.Tensor:
             momentum_beta=0,
             use_nesterov=False,
             weight_decay=0.0,
-            use_decoupled_weight_decay=False,
+            use_decoupled_wd=False,
+            use_independent_wd=False,
             fp32_matmul_prec="highest",
             scaled_orthogonalize_fn=dummy_interleaved_split_orth_fn,
         )
@@ -185,6 +188,35 @@ def test_use_syrk_match_without_syrk(self) -> None:
             ref_param.data,
         )
 
+    def test_use_independent_wd(self) -> None:
+        """Test that use_independent_wd properly decouples weight decay from learning rate."""
+        shape = (32, 32)
+        weight_decay = 0.25
+
+        # Test with independent weight decay: with lr=0, weight decay should still be applied
+        # With lr=0, no gradient update occurs, so param should be exactly (1-wd)*param
+        indep_param = nn.Parameter(torch.randint(-5, 5, shape, dtype=torch.float32, device="cuda"))
+        indep_param_initial = indep_param.data.clone()
+        indep_param.grad = torch.randint_like(indep_param, -5, 5)
+
+        muon_opt_indep = muon.Muon(
+            [indep_param],
+            lr=0.0,  # Zero learning rate
+            weight_decay=weight_decay,
+            use_independent_wd=True,
+            momentum_beta=0.0,
+        )
+        muon_opt_indep.step()
+
+        # With independent weight decay and lr=0, param should be exactly (1-wd)*param
+        expected_param = (1 - weight_decay) * indep_param_initial
+        torch.testing.assert_close(
+            indep_param.data,
+            expected_param,
+            atol=0,
+            rtol=0,
+        )
+
 
 if __name__ == "__main__":
     absltest.main()