Non-commutative inner product support (pygae 426)

Add separate `MultiVector.__ror__` (based on `__or__`), to calculate
inner product from swapped operands. This is NOT commutative operation.

Also add swapped operand operation test to improve pytest coverage.

clifford/_multivector.py

@@ -218,7 +218,21 @@ def __or__(self, other) -> 'MultiVector':
 
         return self._newMV(newValue)
 
-    __ror__ = __or__
+    def __ror__(self, other) -> 'MultiVector':
+        r"""Right-hand inner product, :math:`N \cdot M` """
+
+        other, mv = self._checkOther(other)
+
+        if mv:
+            newValue = self.layout.imt_func(other.value, self.value)
+        else:
+            if isinstance(other, np.ndarray):
+                obj = self.__array__()
+                return other|obj
+            # l * M = M * l = 0 for scalar l
+            return self._newMV(dtype=np.result_type(self.value.dtype, other))
+
+        return self._newMV(newValue)
 
     def __add__(self, other) -> 'MultiVector':
         """ ``self + other``, addition """

clifford/test/test_clifford.py

@@ -741,6 +741,24 @@ def test_right_multiplication_matrix(self, algebra, rng):  # noqa: F811
             res2 = layout.MultiVector(value=b_right@a.value)
             np.testing.assert_almost_equal(res.value, res2.value)
 
+    @pytest.mark.parametrize('func', [
+        operator.add,
+        operator.sub,
+        operator.mul,
+        operator.xor,  # outer product
+        operator.or_,  # inner product
+    ])
+    def test_swapped_operands(self, algebra, rng, func):  # noqa: F811
+        layout = algebra
+        for _ in range(10):
+            mv = layout.randomMV(rng=rng)
+            mv2 = layout.randomMV(rng=rng)
+            # Convert first operand to MVArray. This provokes use of operation with
+            # swapped operands: MultiVector.__rmul__, __ror__, etc.
+            ma = clifford.MVArray(mv)
+            np.testing.assert_equal(func(ma, mv2), func(mv, mv2))
+            np.testing.assert_equal(func(mv2, ma), func(mv2, mv))
+
 
 class TestPrettyRepr:
     """ Test ipython pretty printing, with tidy line wrapping """