docs: update dual mode default from I+ to Iinv+ in docs and changelog

- doc/module-components.rst: update method signature and prose to show Iinv+ as default
- doc/changelog.rst: add bug#514 entry noting the breaking change and migration path
- galgebra/primer.py: update comment to reflect Iinv+ is now the default, not a workaround

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: utiberious

doc/changelog.rst

@@ -8,6 +8,11 @@ Changelog
   \newcommand {\es}[1] {\mathbf{e}_{#1}}
   \newcommand {\til}[1] {\widetilde{#1}}
 
+- :bug:`514` The default dual mode has changed from ``'I+'`` to ``'Iinv+'`` so that
+  ``B * B.dual() == I`` holds for unit blades, matching the standard definition
+  (Doran & Lasenby). To preserve the old behavior, call ``Ga.dual_mode('I+')``
+  at the start of your program.
+
 - :bug:`518` :class:`~galgebra.mv.Mv` now correctly returns ``Mv`` instance when raise to power of zero. But in general, if one needs to call ``Mv`` methods on a result returned by some GA operations, it would be more prudent to initialize it as an ``Mv`` instance first, as sometimes the result becomes a ``sympy`` object.
 
 - :bug:`516` :attr:`~galgebra.mv.Mv.grades` no longer incorrectly returns ``None`` under some circumstances, as now all initialization branch will correctly call :meth:`~galgebra.mv.Mv.characterise_Mv`.

doc/module-components.rst

@@ -339,7 +339,7 @@ If we can instantiate multivectors we can use all the multivector class function
 .. method:: galgebra.mv.Mv.dual()
    :noindex:
 
-   The mode of the ``dual()`` function is set by the ``Ga`` class static member function, ``GA.dual_mode(mode='I+')`` of the ``GA`` geometric galgebra which sets the following return values (:math:`I` is the pseudo-scalar for the geometric algebra ``GA``)
+   The mode of the ``dual()`` function is set by the ``Ga`` class static member function, ``GA.dual_mode(mode='Iinv+')`` of the ``GA`` geometric galgebra which sets the following return values (:math:`I` is the pseudo-scalar for the geometric algebra ``GA``)
 
    =========== ================
    ``mode``    Return Value
@@ -356,7 +356,7 @@ If we can instantiate multivectors we can use all the multivector class function
 
    For example if the geometric algebra is ``o3d``, ``A`` is a multivector in ``o3d``, and we wish to use ``mode='I-'``. We set the mode with the function ``o3d.dual('I-')`` and get the dual of ``A`` with the function ``A.dual()`` which returns :math:`-AI`.
 
-   If ``o3d.dual(mode)`` is not called the default for the dual mode is ``mode='I+'`` and ``A*I`` is returned.
+   If ``o3d.dual(mode)`` is not called the default for the dual mode is ``mode='Iinv+'`` and ``A*I^{-1}`` is returned.
 
    Note that ``Ga.dual(mode)`` used the function ``Ga.I()`` to calculate the normalized pseudoscalar. Thus if the metric tensor is not numerical and orthogonal the correct hint for then ``sig`` input of the *Ga* constructor is required.
 

galgebra/primer.py

@@ -32,9 +32,8 @@
 # Default `Dmode=True` causes partial differentiation
 #   operators to be displayed in shortened form.
 Ga.dual_mode('Iinv+')
-# Sets multivector dualization to be right multiplication by the
-# by the inverse unit pseudoscalar (the convention used in the
-# textbooks LAGA, VAGC, and GACS).
+# Confirms the default dual mode: right multiplication by the inverse
+# pseudoscalar (convention of LAGA, VAGC, and GACS).
 initializations_list = r"""\textsf{The following initialization commands were executed:}\\
 \quad\texttt{from sys import version}\\
 \quad\texttt{import sympy}\\