From: Michael Orlitzky <michael@orlitzky.com>
Date: Tue, 7 Apr 2026 14:56:25 +0000 (-0400)
Subject: mjo/matrix_algebra.py: special case for OctonionAlgebra
X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=64b496b25e36f82a259721b111440bac09a243aa;p=sage.d.git

mjo/matrix_algebra.py: special case for OctonionAlgebra

Eventually I will switch mjo.hurwitz to use Sage's (new)
OctonionAlgebra class. In preparation, add a special case to deal with
the fact that they have a vector() method but no to_vector().
---

diff --git a/mjo/matrix_algebra.py b/mjo/matrix_algebra.py
index 6950b7b..eff1835 100644
--- a/mjo/matrix_algebra.py
+++ b/mjo/matrix_algebra.py
@@ -322,6 +322,30 @@ class MatrixAlgebra(CombinatorialFreeModule):
             sage: A._entry_algebra_element_to_vector(e[7])
             (0, 0, 0, 0, 0, 0, 0, 1)
 
+        Sage OctonionAlgebra. Eventually this should use
+        ``_entry_algebra_gens()`` once we migrate
+        :cls:`OctonionMatrixAlgebra` to Sage's octonions::
+
+            sage: O = OctonionAlgebra(QQ)
+            sage: A = MatrixAlgebra(1, O, QQ)
+            sage: e = A.entry_algebra().basis()
+            sage: A._entry_algebra_element_to_vector(e[0])
+            (1, 0, 0, 0, 0, 0, 0, 0)
+            sage: A._entry_algebra_element_to_vector(e[1])
+            (0, 1, 0, 0, 0, 0, 0, 0)
+            sage: A._entry_algebra_element_to_vector(e[2])
+            (0, 0, 1, 0, 0, 0, 0, 0)
+            sage: A._entry_algebra_element_to_vector(e[3])
+            (0, 0, 0, 1, 0, 0, 0, 0)
+            sage: A._entry_algebra_element_to_vector(e[4])
+            (0, 0, 0, 0, 1, 0, 0, 0)
+            sage: A._entry_algebra_element_to_vector(e[5])
+            (0, 0, 0, 0, 0, 1, 0, 0)
+            sage: A._entry_algebra_element_to_vector(e[6])
+            (0, 0, 0, 0, 0, 0, 1, 0)
+            sage: A._entry_algebra_element_to_vector(e[7])
+            (0, 0, 0, 0, 0, 0, 0, 1)
+
         Sage matrices::
 
             sage: MS = MatrixSpace(QQ,2)
@@ -333,6 +357,10 @@ class MatrixAlgebra(CombinatorialFreeModule):
         if hasattr(entry, 'to_vector'):
             return entry.to_vector()
 
+        if hasattr(entry, 'vector'):
+            # OctonionAlgebra
+            return entry.vector()
+
         from sage.modules.free_module import FreeModule
         d = len(self.entry_algebra_gens())
         V = FreeModule(self.entry_algebra().base_ring(), d)