From: Michael Orlitzky <michael@orlitzky.com>
Date: Wed, 3 Jul 2019 23:47:23 +0000 (-0400)
Subject: eja: add a comment about row/column vectors to eja_sn().
X-Git-Url: http://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=eb48c4d6ce3591d116c85b3f4ab9d1ebb1095367;p=sage.d.git

eja: add a comment about row/column vectors to eja_sn().
---

diff --git a/mjo/eja/euclidean_jordan_algebra.py b/mjo/eja/euclidean_jordan_algebra.py
index f71f75d..c47f400 100644
--- a/mjo/eja/euclidean_jordan_algebra.py
+++ b/mjo/eja/euclidean_jordan_algebra.py
@@ -643,9 +643,13 @@ def eja_sn(dimension, field=QQ):
     W = V.span( mat2vec(s) for s in S )
 
     for s in S:
-        # Brute force the right-multiplication-by-s matrix by looping
+        # Brute force the multiplication-by-s matrix by looping
         # through all elements of the basis and doing the computation
-        # to find out what the corresponding row should be.
+        # to find out what the corresponding row should be. BEWARE:
+        # these multiplication tables won't be symmetric! It therefore
+        # becomes REALLY IMPORTANT that the underlying algebra
+        # constructor uses ROW vectors and not COLUMN vectors. That's
+        # why we're computing rows here and not columns.
         Q_rows = []
         for t in S:
             this_row = mat2vec((s*t + t*s)/2)