eja: fix the natural representation in trivial subalgebras.

[sage.d.git] / mjo / eja / eja_subalgebra.py

diff --git a/mjo/eja/eja_subalgebra.py b/mjo/eja/eja_subalgebra.py
index c82bd1a485c5eb6b82e92134fc30658be4d6d669..2318d12bfd0ebbfc765ca74766af9ab0e73ce02c 100644 (file)
--- a/mjo/eja/eja_subalgebra.py
+++ b/mjo/eja/eja_subalgebra.py
@@ -197,6 +197,30 @@ class FiniteDimensionalEuclideanJordanElementSubalgebra(FiniteDimensionalEuclide
                               natural_basis=natural_basis)
 
 
+    def _a_regular_element(self):
+        """
+        Override the superalgebra method to return the one
+        regular element that is sure to exist in this
+        subalgebra, namely the element that generated it.
+
+        SETUP::
+
+            sage: from mjo.eja.eja_algebra import random_eja
+
+        TESTS::
+
+            sage: set_random_seed()
+            sage: J = random_eja().random_element().subalgebra_generated_by()
+            sage: J._a_regular_element().is_regular()
+            True
+
+        """
+        if self.dimension() == 0:
+            return self.zero()
+        else:
+            return self.monomial(1)
+
+
     def _element_constructor_(self, elt):
         """
         Construct an element of this subalgebra from the given one.
@@ -289,6 +313,18 @@ class FiniteDimensionalEuclideanJordanElementSubalgebra(FiniteDimensionalEuclide
             return self.monomial(self.one_basis())
 
 
+    def natural_basis_space(self):
+        """
+        Return the natural basis space of this algebra, which is identical
+        to that of its superalgebra.
+
+        This is correct "by definition," and avoids a mismatch when the
+        subalgebra is trivial (with no natural basis to infer anything
+        from) and the parent is not.
+        """
+        return self.superalgebra().natural_basis_space()
+
+
     def superalgebra(self):
         """
         Return the superalgebra that this algebra was generated from.