add finite extent to PML for dims where simulation.size == 0

Author: tylerflex

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Web functions create the leading directories for the supplied filename if they don't exist.
 - Some docstring examples that were giving warnings.
 - `web.monitor()` only prints message when condition met.
+- PML boxes have non-zero extent along any dimensions where the simulation has 0 size, to fix plotting issues for 2D simulations.
 
 ## [2.0.2] - 2023-4-3
 

tests/test_components/test_simulation.py

@@ -1500,3 +1500,34 @@ def test_sim_volumetric_structures():
         )
     with pytest.raises(Exception):
         _ = td.Structure(geometry=td.Sphere(radius=1), medium=box.medium)
+
+
+@pytest.mark.parametrize("normal_axis", (0, 1, 2))
+def test_pml_boxes_2D(normal_axis):
+    """Ensure pml boxes have non-zero dimension for 2D sim."""
+
+    sim_size = [1, 1, 1]
+    sim_size[normal_axis] = 0
+    pml_on_kwargs = {dim: axis != normal_axis for axis, dim in enumerate("xyz")}
+
+    sim2d = td.Simulation(
+        size=sim_size,
+        run_time=1e-12,
+        grid_spec=td.GridSpec(wavelength=1.0),
+        sources=[
+            td.PointDipole(
+                center=(0, 0, 0),
+                polarization="Ex",
+                source_time=td.GaussianPulse(
+                    freq0=1e14,
+                    fwidth=1e12,
+                ),
+            )
+        ],
+        boundary_spec=td.BoundarySpec.pml(**pml_on_kwargs),
+    )
+
+    pml_boxes = sim2d._make_pml_boxes(normal_axis=normal_axis)
+
+    for pml_box in pml_boxes:
+        assert pml_box.size[normal_axis] > 0, "PML box has size of 0 in normal direction of 2D sim."

tidy3d/components/simulation.py

@@ -61,6 +61,9 @@
 # equal to this times the grid size
 DIST_NEIGHBOR_REL_2D_MED = 1e-5
 
+# height of the PML plotting boxes along any dimensions where sim.size[dim] == 0
+PML_HEIGHT_FOR_0_DIMS = 0.02
+
 
 class Simulation(Box):  # pylint:disable=too-many-public-methods
     """Contains all information about Tidy3d simulation.
@@ -1772,7 +1775,16 @@ def _make_pml_box(self, pml_axis: Axis, pml_height: float, sign: int) -> Box:
             rmax[pml_axis] = rmin[pml_axis] + pml_height
         else:
             rmin[pml_axis] = rmax[pml_axis] - pml_height
-        return Box.from_bounds(rmin=rmin, rmax=rmax)
+        pml_box = Box.from_bounds(rmin=rmin, rmax=rmax)
+
+        # if any dimension of the sim has size 0, set the PML to a very small size along that dim
+        new_size = list(pml_box.size)
+        for dim_index, sim_size in enumerate(self.size):
+            if sim_size == 0.0:
+                new_size[dim_index] = PML_HEIGHT_FOR_0_DIMS
+        pml_box = pml_box.updated_copy(size=new_size)
+
+        return pml_box
 
     @equal_aspect
     @add_ax_if_none