From 2490f922d606dd4b4e4a6e4152ff8edd20f3c15c Mon Sep 17 00:00:00 2001
From: Casey Wojcik <charles@flexcompute.com>
Date: Wed, 13 Nov 2024 11:07:12 +0000
Subject: [PATCH] Validate against nonlinear and modulation in
 FullyAnisotropicMedium.from_diagonal

---
 CHANGELOG.md                         |  1 +
 tests/test_components/test_medium.py | 32 ++++++++++++++++++++++++++++
 tidy3d/components/medium.py          | 12 +++++++++++
 3 files changed, 45 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index dc94d0da5..f6454f51b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -27,6 +27,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Some failing examples in the expressions plugin documentation.
 - Inaccuracy in transforming gradients from edge to `PolySlab.vertices`.
 - Bug in `run_async` where an adjoint simulation would sometimes be assigned to the wrong forward simulation.
+- Validate against nonlinearity or modulation in `FullyAnisotropicMedium.from_diagonal`.
 
 
 ## [2.7.6] - 2024-10-30
diff --git a/tests/test_components/test_medium.py b/tests/test_components/test_medium.py
index 1b9eafaab..2b54ad76b 100644
--- a/tests/test_components/test_medium.py
+++ b/tests/test_components/test_medium.py
@@ -516,6 +516,38 @@ def test_fully_anisotropic_media():
     assert all(np.isin(np.round(perm_d), np.round(np.diag(perm_diag))))
     assert all(np.isin(np.round(cond_d), np.round(np.diag(cond_diag))))
 
+    with pytest.raises(ValidationError):
+        _ = td.FullyAnisotropicMedium.from_diagonal(
+            xx=td.Medium(
+                permittivity=2,
+                nonlinear_spec=td.NonlinearSpec(
+                    models=[
+                        td.NonlinearSusceptibility(chi3=2),
+                        td.TwoPhotonAbsorption(beta=1.3),
+                        td.KerrNonlinearity(n2=1.3),
+                    ]
+                ),
+            ),
+            yy=td.Medium(permittivity=4),
+            zz=td.Medium(permittivity=1),
+            rotation=td.RotationAroundAxis(axis=2, angle=np.pi / 4),
+        )
+
+    with pytest.raises(ValidationError):
+        _ = td.FullyAnisotropicMedium.from_diagonal(
+            xx=td.Medium(permittivity=2),
+            yy=td.Medium(
+                permittivity=4,
+                modulation_spec=td.ModulationSpec(
+                    permittivity=td.SpaceTimeModulation(
+                        time_modulation=td.ContinuousWaveTimeModulation(freq0=1e12, amplitude=0.02)
+                    )
+                ),
+            ),
+            zz=td.Medium(permittivity=1),
+            rotation=td.RotationAroundAxis(axis=2, angle=np.pi / 4),
+        )
+
 
 def test_nonlinear_medium(log_capture):
     med = td.Medium(
diff --git a/tidy3d/components/medium.py b/tidy3d/components/medium.py
index 5e60901fc..0d353aca7 100644
--- a/tidy3d/components/medium.py
+++ b/tidy3d/components/medium.py
@@ -5191,6 +5191,18 @@ def from_diagonal(cls, xx: Medium, yy: Medium, zz: Medium, rotation: RotationTyp
             Resulting fully anisotropic medium.
         """
 
+        if any(comp.nonlinear_spec is not None for comp in [xx, yy, zz]):
+            raise ValidationError(
+                "Nonlinearities are not currently supported for the components "
+                "of a fully anisotropic medium."
+            )
+
+        if any(comp.modulation_spec is not None for comp in [xx, yy, zz]):
+            raise ValidationError(
+                "Modulation is not currently supported for the components "
+                "of a fully anisotropic medium."
+            )
+
         permittivity_diag = np.diag([comp.permittivity for comp in [xx, yy, zz]]).tolist()
         conductivity_diag = np.diag([comp.conductivity for comp in [xx, yy, zz]]).tolist()