From 7ed6bf090129906021f0c3c4aaa2f7e24086e210 Mon Sep 17 00:00:00 2001
From: Florian Pfaff <6773539+FlorianPfaff@users.noreply.github.com>
Date: Thu, 6 Aug 2026 15:05:57 +0800
Subject: [PATCH 1/2] Validate hypertoroidal Fourier coefficient counts

---
 src/pyrecest/filters/hypertoroidal_fourier_filter.py | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/pyrecest/filters/hypertoroidal_fourier_filter.py b/src/pyrecest/filters/hypertoroidal_fourier_filter.py
index a198df740e..9e045b3f01 100644
--- a/src/pyrecest/filters/hypertoroidal_fourier_filter.py
+++ b/src/pyrecest/filters/hypertoroidal_fourier_filter.py
@@ -20,6 +20,7 @@
 )
 from pyrecest.distributions.hypertorus.hypertoroidal_fourier_distribution import (
     HypertoroidalFourierDistribution,
+    _normalize_coefficient_shape,
 )
 
 from .abstract_filter import AbstractFilter
@@ -56,9 +57,11 @@ def __init__(self, n_coefficients, transformation="sqrt"):
                 "HypertoroidalFourierFilter is not supported on the "
                 f"{pyrecest.backend.__backend_name__} backend."
             )
-        if isinstance(n_coefficients, int):
-            n_coefficients = (n_coefficients,)
-        n_coefficients = tuple(int(n) for n in n_coefficients)
+        n_coefficients = _normalize_coefficient_shape(
+            n_coefficients,
+            "n_coefficients",
+            require_odd=True,
+        )
         dim = len(n_coefficients)
 
         # Build a uniform HFD directly (only the DC component is non-zero)

From 0002c8686e23d3dae92b68d801e978df43491d00 Mon Sep 17 00:00:00 2001
From: Florian Pfaff <6773539+FlorianPfaff@users.noreply.github.com>
Date: Thu, 6 Aug 2026 15:06:08 +0800
Subject: [PATCH 2/2] Add Fourier coefficient validation regression tests

---
 ...l_fourier_filter_coefficient_validation.py | 39 +++++++++++++++++++
 1 file changed, 39 insertions(+)
 create mode 100644 tests/filters/test_hypertoroidal_fourier_filter_coefficient_validation.py

diff --git a/tests/filters/test_hypertoroidal_fourier_filter_coefficient_validation.py b/tests/filters/test_hypertoroidal_fourier_filter_coefficient_validation.py
new file mode 100644
index 0000000000..d64d062f4a
--- /dev/null
+++ b/tests/filters/test_hypertoroidal_fourier_filter_coefficient_validation.py
@@ -0,0 +1,39 @@
+import unittest
+
+import numpy as np
+
+import pyrecest.backend
+from pyrecest.filters.hypertoroidal_fourier_filter import HypertoroidalFourierFilter
+
+
+@unittest.skipIf(
+    pyrecest.backend.__backend_name__ in ("jax", "pytorch"),
+    reason="HypertoroidalFourierFilter is not supported on this backend",
+)
+class TestHypertoroidalFourierFilterCoefficientValidation(unittest.TestCase):
+    def test_accepts_numpy_integer_scalar(self):
+        fourier_filter = HypertoroidalFourierFilter(np.int64(11))
+
+        self.assertEqual(fourier_filter.filter_state.coeff_mat.shape, (11,))
+
+    def test_rejects_values_that_would_be_silently_reinterpreted(self):
+        invalid_values = (
+            True,
+            "11",
+            (),
+            (11.5,),
+            (11.0,),
+        )
+
+        for value in invalid_values:
+            with self.subTest(value=value):
+                with self.assertRaises((TypeError, ValueError)):
+                    HypertoroidalFourierFilter(value)
+
+    def test_rejects_nonpositive_or_even_coefficient_counts(self):
+        invalid_values = (0, -1, 10, (11, 0), (11, 12))
+
+        for value in invalid_values:
+            with self.subTest(value=value):
+                with self.assertRaisesRegex(ValueError, "n_coefficients"):
+                    HypertoroidalFourierFilter(value)