mjo/clan/jordan_spin_clan.py: add a comment about the inner product

diff --git a/mjo/clan/jordan_spin_clan.py b/mjo/clan/jordan_spin_clan.py
index 5d836d046fd58e0020290b0f15dc45907ed2809e..7eabc84eba5f6285b7d730c718d40f9cfd013876 100644 (file)
--- a/mjo/clan/jordan_spin_clan.py
+++ b/mjo/clan/jordan_spin_clan.py
@@ -102,8 +102,15 @@ class JordanSpinClan(NormalDecomposition):
             return RN.from_vector(V(z_coords))
 
         def ip(x,y):
+            # The Ishi inner product. That this is NOT the Euclidean
+            # inner product on coordinates, because (from cp(x,y)
+            # above) this one is,
+            #
+            #   x11*y11 + x22*y22 + 2<x21,y21>
+            #
+            # (The off-diagonals are weighted more than usual.)
             p = cp(x,y) / two
-            return p[(0,0,1)] + p[(1,1,1)]  # sum of diagonals
+            return p[(0,0,1)] + p[(1,1,1)]
 
         super().__init__(RN, cp, ip, **kwargs)