fix[adjoint]: select proper shape for CustomMedium derivatives when eps_data has a frequency dimension with multiple entries

Author: Gregory Roberts

CHANGELOG.md

@@ -18,13 +18,15 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - Fixed bug in broadband adjoint source creation when forward simulation had a pulse amplitude greater than 1 or a nonzero pulse phase.
+- Fixed shaping of `CustomMedium` gradients when permittivity data includes a frequency dimension with multiple entries.
 
 ### Changed
 - Relaxed bounds checking of path integrals during `WavePort` validation.
 - Internal adjoint helper methods are now prefixed with an underscore to separate them from the public API.
 - Drop the dependency on `gdspy`, which has been unmaintained for over two years. Interfaces previously relying on `gdspy` now use its maintained successor, `gdstk`, with equivalent functionality.
 - Small (around 1e-4) numerical precision improvements in EME solver.
 - Adjoint source frequency width is adjusted to decay sufficiently before zero frequency when possible to improve accuracy of simulation normalization when using custom current sources.
+- Change `VisualizationSpec` validator for checking validity of user specified colors to only issue a warning if matplotlib is not installed instead of an error.
 
 ## [2.8.4] - 2025-05-15
 

tidy3d/components/medium.py

@@ -1672,6 +1672,8 @@ def _derivative_field_cmp(
         coords_interp = {key: val for key, val in eps_data.coords.items() if len(val) > 1}
         dims_sum = {dim for dim in eps_data.coords.keys() if dim not in coords_interp}
 
+        eps_coordinate_shape = [len(eps_data.coords[dim]) for dim in eps_data.dims if dim in "xyz"]
+
         # compute sizes along each of the interpolation dimensions
         sizes_list = []
         for _, coords in coords_interp.items():
@@ -1703,7 +1705,7 @@ def _derivative_field_cmp(
             E_der_dim.interp(**coords_interp, assume_sorted=True).fillna(0.0).sum(dims_sum).sum("f")
         )
         vjp_array = np.array(E_der_dim_interp.values).astype(complex)
-        vjp_array = vjp_array.reshape(eps_data.shape)
+        vjp_array = vjp_array.reshape(eps_coordinate_shape)
 
         # multiply by volume elements (if possible, being defensive here..)
         try:
@@ -2871,10 +2873,11 @@ def _derivative_field_cmp(
         freqs: NDArray,
     ) -> np.ndarray:
         """Compute derivative with respect to the ``dim`` components within the custom medium."""
-
         coords_interp = {key: eps_data.coords[key] for key in "xyz"}
         coords_interp = {key: val for key, val in coords_interp.items() if len(val) > 1}
 
+        eps_coordinate_shape = [len(eps_data.coords[dim]) for dim in eps_data.dims if dim in "xyz"]
+
         E_der_dim_interp = E_der_map[f"E{dim}"].sel(f=freqs)
 
         for dim_ in "xyz":
@@ -2928,7 +2931,7 @@ def _derivative_field_cmp(
                 "message and some information about your simulation setup and we will investigate. "
             )
         vjp_array = E_der_dim_interp.values
-        vjp_array = vjp_array.reshape(eps_data.shape)
+        vjp_array = vjp_array.reshape(eps_coordinate_shape)
 
         return vjp_array