fix(interop): reset dual mode to galgebra default in interop.Cl

galgebra/interop/_cl.py

@@ -16,6 +16,15 @@ def Cl(p: int, q: int = 0, r: int = 0, root: str = 'e', **kwargs):
     Uses galgebra defaults (basis numbered from 1, dual mode ``'I+'``).
     For kingdon conventions, use ``galgebra.interop.kingdon.Cl`` instead.
 
+    .. note::
+
+        This function resets the session-wide dual mode to ``'I+'``
+        (galgebra default) before building the algebra.  If you have
+        previously called ``galgebra.interop.kingdon.Cl`` in the same
+        session, that call will have set ``'Iinv+'`` globally; this call
+        restores the galgebra default.  See :issue:`555` for the
+        long-term per-instance fix.
+
     Parameters
     ----------
     p : int
@@ -52,6 +61,9 @@ def Cl(p: int, q: int = 0, r: int = 0, root: str = 'e', **kwargs):
     if n == 0:
         raise ValueError("Total dimension p + q + r must be positive.")
 
+    # Reset to galgebra default dual convention
+    Ga.dual_mode('I+')
+
     # Build diagonal metric: p ones, q negative ones, r zeros
     g = [1] * p + [-1] * q + [0] * r
 

galgebra/interop/kingdon.py

@@ -20,11 +20,15 @@ def Cl(p: int, q: int = 0, r: int = 0, root: str = 'e', **kwargs):
     - **Basis naming**: uses 0-indexed names (``e_0, e_1, ...``) to match
       kingdon's default for PGA algebras.
 
-    .. warning::
-
-        The dual mode change is session-wide.  If you mix kingdon and
-        galgebra conventions in the same session, save and restore
-        ``Ga.dual_mode_value`` around the kingdon block::
+    .. note::
+
+        This function sets the session-wide dual mode to ``'Iinv+'``
+        before building the algebra.  ``galgebra.interop.Cl`` resets it
+        back to ``'I+'``.  This means any algebra built under ``'Iinv+'``
+        will compute duals with ``'I+'`` once a subsequent
+        ``galgebra.interop.Cl`` call is made.  For full isolation over a
+        block of kingdon-convention code, save and restore
+        ``Ga.dual_mode_value`` manually::
 
             saved = Ga.dual_mode_value
             try:

test/test_test.py

@@ -734,3 +734,18 @@ def test_Cl_kingdon(self):
             assert Ga.dual_mode_value == 'Iinv+'
         finally:
             Ga.dual_mode(saved)
+
+    def test_Cl_dual_mode_reset(self):
+        """galgebra.interop.Cl must reset dual mode to I+ after kingdon.Cl set Iinv+."""
+        from galgebra.interop.kingdon import Cl as KCl
+        from galgebra.interop import Cl
+        from galgebra.ga import Ga
+
+        saved = Ga.dual_mode_value
+        try:
+            KCl(3)
+            assert Ga.dual_mode_value == 'Iinv+'
+            Cl(3)
+            assert Ga.dual_mode_value == 'I+'
+        finally:
+            Ga.dual_mode(saved)