Fix bug when symmetry + non-symmetric boundary conditions are defined

Author: momchil-flex

tidy3d/components/grid/grid_spec.py

@@ -90,16 +90,19 @@ def make_coords(
         )
 
         # incorporate symmetries
+        n_pml = list(num_pml_layers)
         if symmetry[axis] != 0:
             # Offset to center if symmetry present
             center = structures[0].geometry.center[axis]
             center_ind = np.argmin(np.abs(center - bound_coords))
             bound_coords += center - bound_coords[center_ind]
             bound_coords = bound_coords[bound_coords >= center]
             bound_coords = np.append(2 * center - bound_coords[:0:-1], bound_coords)
+            # Apply PMLs on the - side as they are defined on the + side
+            n_pml[0] = n_pml[1]
 
         # Add PML layers in using dl on edges
-        bound_coords = self._add_pml_to_bounds(num_pml_layers, bound_coords)
+        bound_coords = self._add_pml_to_bounds(n_pml, bound_coords)
         return bound_coords
 
     @abstractmethod