Fail for registers with differentiable coordinates

pulser-core/pulser/register/register.py

@@ -344,6 +344,8 @@ def with_automatic_layout(
         Raises:
             RuntimeError: If the automatic layout generation fails to meet
                 the device constraints.
+            NotImplementedError: When the register has differentiable
+                quantities (ie torch Tensors with requires_grad=True).
 
         Returns:
             Register: A new register instance with identical qubit IDs and
@@ -353,6 +355,15 @@ def with_automatic_layout(
             raise TypeError(
                 f"'device' must be of type Device, not {type(device)}."
             )
+        if (
+            self._coords_arr.is_tensor
+            and self._coords_arr.as_tensor().requires_grad
+        ):
+            raise NotImplementedError(
+                "'Register.with_automatic_layout()' does not support "
+                "registers with differentiable coordinates."
+            )
+
         trap_coords = generate_trap_coordinates(
             self.sorted_coords,
             min_trap_dist=device.min_atom_distance,

tests/test_register.py

@@ -659,3 +659,14 @@ def test_automatic_layout(optimal_filling):
         big_reg.with_automatic_layout(device).layout.number_of_traps
         >= min_traps
     )
+
+
+def test_automatic_layout_diff():
+    torch = pytest.importorskip("torch")
+    with pytest.raises(
+        NotImplementedError,
+        match="does not support registers with differentiable coordinates",
+    ):
+        Register.square(
+            2, spacing=torch.tensor(10.0, requires_grad=True)
+        ).with_automatic_layout(AnalogDevice)