From b82bd087507b8f727c10ca0eb55f9a1d15ed3438 Mon Sep 17 00:00:00 2001
From: Michael Orlitzky <michael@orlitzky.com>
Date: Sat, 20 Jul 2019 23:03:20 -0400
Subject: [PATCH] eja: turn the eja_rn() constructor into a class too.

This fixes the inner product issue I created in the previous commit.
We can always get rid of this class when real Cartesian products are
supported.
---
 mjo/eja/euclidean_jordan_algebra.py | 50 ++++++++++++++---------------
 1 file changed, 25 insertions(+), 25 deletions(-)

diff --git a/mjo/eja/euclidean_jordan_algebra.py b/mjo/eja/euclidean_jordan_algebra.py
index e109b52..15ff26c 100644
--- a/mjo/eja/euclidean_jordan_algebra.py
+++ b/mjo/eja/euclidean_jordan_algebra.py
@@ -922,7 +922,7 @@ class FiniteDimensionalEuclideanJordanAlgebra(FiniteDimensionalAlgebra):
             TESTS::
 
                 sage: set_random_seed()
-                sage: J = eja_rn(5)
+                sage: J = RealCartesianProductEJA(5)
                 sage: c = J.random_element().subalgebra_idempotent()
                 sage: c^2 == c
                 True
@@ -1006,16 +1006,20 @@ class FiniteDimensionalEuclideanJordanAlgebra(FiniteDimensionalAlgebra):
             return (self*other).trace()
 
 
-def eja_rn(dimension, field=QQ):
+class RealCartesianProductEJA(FiniteDimensionalEuclideanJordanAlgebra):
     """
     Return the Euclidean Jordan Algebra corresponding to the set
     `R^n` under the Hadamard product.
 
+    Note: this is nothing more than the Cartesian product of ``n``
+    copies of the spin algebra. Once Cartesian product algebras
+    are implemented, this can go.
+
     EXAMPLES:
 
     This multiplication table can be verified by hand::
 
-        sage: J = eja_rn(3)
+        sage: J = RealCartesianProductEJA(3)
         sage: e0,e1,e2 = J.gens()
         sage: e0*e0
         e0
@@ -1031,18 +1035,21 @@ def eja_rn(dimension, field=QQ):
         e2
 
     """
-    # The FiniteDimensionalAlgebra constructor takes a list of
-    # matrices, the ith representing right multiplication by the ith
-    # basis element in the vector space. So if e_1 = (1,0,0), then
-    # right (Hadamard) multiplication of x by e_1 picks out the first
-    # component of x; and likewise for the ith basis element e_i.
-    Qs = [ matrix(field, dimension, dimension, lambda k,j: 1*(k == j == i))
-           for i in xrange(dimension) ]
+    @staticmethod
+    def __classcall_private__(cls, n, field=QQ):
+        # The FiniteDimensionalAlgebra constructor takes a list of
+        # matrices, the ith representing right multiplication by the ith
+        # basis element in the vector space. So if e_1 = (1,0,0), then
+        # right (Hadamard) multiplication of x by e_1 picks out the first
+        # component of x; and likewise for the ith basis element e_i.
+        Qs = [ matrix(field, n, n, lambda k,j: 1*(k == j == i))
+               for i in xrange(n) ]
 
-    return FiniteDimensionalEuclideanJordanAlgebra(field,
-                                                   Qs,
-                                                   rank=dimension)
+        fdeja = super(RealCartesianProductEJA, cls)
+        return fdeja.__classcall_private__(cls, field, Qs, rank=n)
 
+    def inner_product(self, x, y):
+        return _usual_ip(x,y)
 
 
 def random_eja():
@@ -1078,7 +1085,7 @@ def random_eja():
 
     """
     n = ZZ.random_element(1,5)
-    constructor = choice([eja_rn,
+    constructor = choice([RealCartesianProductEJA,
                           JordanSpinEJA,
                           RealSymmetricEJA,
                           ComplexHermitianEJA,
@@ -1679,18 +1686,11 @@ class JordanSpinEJA(FiniteDimensionalEuclideanJordanAlgebra):
             Qi[0,0] = Qi[0,0] * ~field(2)
             Qs.append(Qi)
 
+        # The rank of the spin algebra is two, unless we're in a
+        # one-dimensional ambient space (because the rank is bounded by
+        # the ambient dimension).
         fdeja = super(JordanSpinEJA, cls)
-        return fdeja.__classcall_private__(cls, field, Qs)
-
-    def rank(self):
-        """
-        Return the rank of this Jordan Spin Algebra.
-
-        The rank of the spin algebra is two, unless we're in a
-        one-dimensional ambient space (because the rank is bounded by
-        the ambient dimension).
-        """
-        return min(self.dimension(),2)
+        return fdeja.__classcall_private__(cls, field, Qs, rank=min(n,2))
 
     def inner_product(self, x, y):
         return _usual_ip(x,y)
-- 
2.44.2