fix: resolve scalar frequencies in metrics not passing validation

CHANGELOG.md

@@ -9,18 +9,16 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 - Users can manually specify the background medium for a structure to be used for geometry gradient calculations by supplying `Structure.background_permittivity`. This is useful when there are overlapping structures or structures embedded in other mediums.
-
-### Fixed
-- Minor gradient direction and normalization fixes for polyslab, field monitors, and diffraction monitors in autograd.
-- Resolved an issue where temporary files for adjoint simulations were not being deleted properly.
 - Autograd functions can now be called directly on `DataArray` (e.g., `np.sum(data_array)`) in objective functions.
 
 ### Changed
 - Improved autograd tracer handling in `DataArray`, resulting in significant speedups for differentiation involving large monitors.
 
 ### Fixed
+- Minor gradient direction and normalization fixes for polyslab, field monitors, and diffraction monitors in autograd.
+- Resolved an issue where temporary files for adjoint simulations were not being deleted properly.
 - Resolve several edge cases where autograd boxes were incorrectly converted to numpy arrays.
-
+- Resolve issue where scalar frequencies in metric definitions (`ModeAmp(f=freq)` instead of `ModeAmp(f=[freq])`) would erroneously fail validation.
 
 ## [2.7.5] - 2024-10-16
 

tests/test_plugins/test_invdes.py

@@ -586,6 +586,16 @@ def test_initial_simulation_multi():
         )
 
 
+def test_metric_scalar_freq():
+    invdes = make_invdes()
+    metric = ModePower(monitor_name=MNT_NAME2, mode_index=0, f=FREQ0)
+    monitor = mnt2.updated_copy(freqs=[FREQ0, FREQ0 / 2])
+    invdes = invdes.updated_copy(
+        metric=metric,
+        simulation=simulation.updated_copy(monitors=[monitor]),
+    )
+
+
 def test_validate_invdes_metric():
     """Test the _validate_metric_monitor_name validator."""
     invdes = make_invdes()

tidy3d/plugins/expressions/metrics.py

@@ -93,7 +93,7 @@ def from_mode_monitor(
     @property
     def _validation_data(self) -> Any:
         """Return dummy data for this metric (complex array of mode amplitudes)."""
-        f = list(self.f) if self.f is not None else [1.0]
+        f = np.atleast_1d(self.f).tolist() if self.f is not None else [1.0]
         amps_data = np.random.rand(len(f)) + 1j * np.random.rand(len(f))
         amps = xr.DataArray(
             amps_data.reshape(1, 1, -1),
@@ -111,7 +111,8 @@ def evaluate(self, *args: Any, **kwargs: Any) -> NumberType:
             direction=self.direction, mode_index=self.mode_index
         )
         if self.f is not None:
-            amps = amps.sel(f=list(self.f), method="nearest")
+            f = list(self.f) if isinstance(self.f, tuple) else self.f
+            amps = amps.sel(f=f, method="nearest")
         return np.squeeze(amps.data)