+class CartesianProductParentEJAElement(FiniteDimensionalEJAElement):
+ r"""
+ An intermediate class for elements that have a Cartesian
+ product as their parent algebra.
+
+ This is needed because the ``to_matrix`` method (which gives you a
+ representation from the superalgebra) needs to do special stuff
+ for Cartesian products. Specifically, an EJA subalgebra of a
+ Cartesian product EJA will not itself be a Cartesian product (it
+ has its own basis) -- but we want ``to_matrix()`` to be able to
+ give us a Cartesian product representation.
+ """
+ def to_matrix(self):
+ # An override is necessary to call our custom _scale().
+ B = self.parent().matrix_basis()
+ W = self.parent().matrix_space()
+
+ # Aaaaand linear combinations don't work in Cartesian
+ # product spaces, even though they provide a method with
+ # that name. This is hidden in a subclass because the
+ # _scale() function is slow.
+ pairs = zip(B, self.to_vector())
+ return W.sum( _scale(b, alpha) for (b,alpha) in pairs )
+
+class CartesianProductEJAElement(CartesianProductParentEJAElement):