Fix up dot/cross wrapper for non-multiplicative units

2 files changed, 67 insertions, 2 deletions

diff --git a/pint/facets/numpy/numpy_func.py b/pint/facets/numpy/numpy_func.py
index 2a004a8..f25f4a4 100644
--- a/pint/facets/numpy/numpy_func.py
+++ b/pint/facets/numpy/numpy_func.py
@@ -729,6 +729,7 @@ for name in ["prod", "nanprod"]:
     implement_prod_func(name)
 
 
+# Handle mutliplicative functions separately to deal with non-multiplicative units
 def _base_unit_if_needed(a):
     if a._is_multiplicative:
         return a
@@ -759,6 +760,30 @@ def _trapz(a, x=None, dx=1.0, **kwargs):
     return a.units._REGISTRY.Quantity(ret, units)
 
 
+def implement_mul_func(func):
+    # If NumPy is not available, do not attempt implement that which does not exist
+    if np is None:
+        return
+
+    func = getattr(np, func_str)
+
+    @implements(func_str, "function")
+    def implementation(a, b, **kwargs):
+        a = _base_unit_if_needed(a)
+        units = a.units
+        if hasattr(b, "units"):
+            b = _base_unit_if_needed(b)
+            units *= b.units
+            b = b._magnitude
+
+        mag = func(a._magnitude, b, **kwargs)
+        return a.units._REGISTRY.Quantity(mag, units)
+
+
+for func_str in ["cross", "dot"]:
+    implement_mul_func(func_str)
+
+
 # Implement simple matching-unit or stripped-unit functions based on signature
 
 
@@ -950,8 +975,6 @@ for func_str in [
 # Handle functions with output unit defined by operation
 for func_str in ["std", "nanstd", "sum", "nansum", "cumsum", "nancumsum"]:
     implement_func("function", func_str, input_units=None, output_unit="sum")
-for func_str in ["cross", "dot"]:
-    implement_func("function", func_str, input_units=None, output_unit="mul")
 for func_str in ["diff", "ediff1d"]:
     implement_func("function", func_str, input_units=None, output_unit="delta")
 for func_str in ["gradient"]:
diff --git a/pint/testsuite/test_numpy_func.py b/pint/testsuite/test_numpy_func.py
index 4f1488c..7a0cdb7 100644
--- a/pint/testsuite/test_numpy_func.py
+++ b/pint/testsuite/test_numpy_func.py
@@ -213,3 +213,45 @@ class TestNumPyFuncUtils(TestNumpyMethods):
         z = self.Q_(np.array([0.0, 2.0, 4.0]), "m")
         with pytest.raises(OffsetUnitCalculusError):
             np.trapz(t, x=z)
+
+    def test_dot(self):
+        with ExitStack() as stack:
+            stack.callback(
+                setattr,
+                self.ureg,
+                "autoconvert_offset_to_baseunit",
+                self.ureg.autoconvert_offset_to_baseunit,
+            )
+            self.ureg.autoconvert_offset_to_baseunit = True
+            t = self.Q_(np.array([0.0, 5.0, 10.0]), "degC")
+            z = self.Q_(np.array([1.0, 2.0, 3.0]), "m")
+            helpers.assert_quantity_almost_equal(
+                np.dot(t, z), self.Q_(1678.9, "kelvin meter")
+            )
+
+    def test_dot_no_autoconvert(self):
+        t = self.Q_(np.array([0.0, 5.0, 10.0]), "degC")
+        z = self.Q_(np.array([1.0, 2.0, 3.0]), "m")
+        with pytest.raises(OffsetUnitCalculusError):
+            np.dot(t, z)
+
+    def test_cross(self):
+        with ExitStack() as stack:
+            stack.callback(
+                setattr,
+                self.ureg,
+                "autoconvert_offset_to_baseunit",
+                self.ureg.autoconvert_offset_to_baseunit,
+            )
+            self.ureg.autoconvert_offset_to_baseunit = True
+            t = self.Q_(np.array([0.0, 5.0, 10.0]), "degC")
+            z = self.Q_(np.array([1.0, 2.0, 3.0]), "m")
+            helpers.assert_quantity_almost_equal(
+                np.cross(t, z), self.Q_([268.15, -536.3, 268.15], "kelvin meter")
+            )
+
+    def test_cross_no_autoconvert(self):
+        t = self.Q_(np.array([0.0, 5.0, 10.0]), "degC")
+        z = self.Q_(np.array([1.0, 2.0, 3.0]), "m")
+        with pytest.raises(OffsetUnitCalculusError):
+            np.cross(t, z)