Correct backend dot behavior

src/pyrecest/backend_support/_pytorch_dot_outer_device_contract.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 
+# Keep this hook aligned with the backend dot tests.
 def _preferred_pytorch_device(torch_module, *values):
     """Return a non-CPU tensor device when mixed-device operands are present."""
     for value in values:
@@ -52,8 +53,8 @@ def dot(a, b):
         a, b = _promoted_pair(raw_pytorch, torch, a, b)
         if a.ndim == 0 or b.ndim == 0:
             return torch.multiply(a, b)
-        if a.ndim == 1 and b.ndim == 1:
-            return torch.dot(a, b)
+        if a.ndim <= 2 and b.ndim <= 2:
+            return torch.matmul(a, b)
         if b.ndim == 1:
             return torch.einsum("...i,i->...", a, b)
         if a.ndim == 1:

tests/backend_support/test_pytorch_dot_matrix_contract.py

@@ -0,0 +1,27 @@
+import importlib.util
+
+import pytest
+
+from tests.support.backend_runner import run_backend_code
+
+pytestmark = pytest.mark.backend_portable
+
+
+def test_public_pytorch_dot_matches_matrix_product_shape():
+    if importlib.util.find_spec("torch") is None:
+        pytest.skip("PyTorch is not installed")
+
+    code = """
+import pyrecest.backend as backend
+
+left = backend.array([[1.0, 2.0], [3.0, 4.0]])
+right = backend.array([[5.0, 6.0], [7.0, 8.0]])
+result = backend.dot(left, right)
+assert tuple(result.shape) == (2, 2)
+assert backend.to_numpy(result).tolist() == [[19.0, 22.0], [43.0, 50.0]]
+print("ok")
+"""
+    result = run_backend_code("pytorch", code)
+
+    assert result.returncode == 0, result.stderr
+    assert "ok" in result.stdout