X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Feja%2Feuclidean_jordan_algebra.py;h=be281bfb99d0ef86e73fa7d4a2d3643f54d605e3;hb=83f719b66100fdb5bf5035355c48b5337be6b11e;hp=5ccf2f29fd480f4a499d55fc3d9dad85942dc6f4;hpb=99a85a92ed375722e51f7842dcc8d370b134629b;p=sage.d.git

diff --git a/mjo/eja/euclidean_jordan_algebra.py b/mjo/eja/euclidean_jordan_algebra.py
index 5ccf2f2..be281bf 100644
--- a/mjo/eja/euclidean_jordan_algebra.py
+++ b/mjo/eja/euclidean_jordan_algebra.py
@@ -7,10 +7,37 @@ what can be supported in a general Jordan Algebra.
 
 from sage.all import *
 
+def eja_minimal_polynomial(x):
+    """
+    Return the minimal polynomial of ``x`` in its parent EJA
+    """
+    return x._x.matrix().minimal_polynomial()
+
+
 def eja_rn(dimension, field=QQ):
     """
     Return the Euclidean Jordan Algebra corresponding to the set
     `R^n` under the Hadamard product.
+
+    EXAMPLES:
+
+    This multiplication table can be verified by hand::
+
+        sage: J = eja_rn(3)
+        sage: e0,e1,e2 = J.gens()
+        sage: e0*e0
+        e0
+        sage: e0*e1
+        0
+        sage: e0*e2
+        0
+        sage: e1*e1
+        e1
+        sage: e1*e2
+        0
+        sage: e2*e2
+        e2
+
     """
     # The FiniteDimensionalAlgebra constructor takes a list of
     # matrices, the ith representing right multiplication by the ith
@@ -21,3 +48,54 @@ def eja_rn(dimension, field=QQ):
            for i in xrange(dimension) ]
     A = FiniteDimensionalAlgebra(QQ,Qs,assume_associative=True)
     return JordanAlgebra(A)
+
+
+def eja_ln(dimension, field=QQ):
+    """
+    Return the Jordan algebra corresponding to the Lorenzt "ice cream"
+    cone of the given ``dimension``.
+
+    EXAMPLES:
+
+    This multiplication table can be verified by hand::
+
+        sage: J = eja_ln(4)
+        sage: e0,e1,e2,e3 = J.gens()
+        sage: e0*e0
+        e0
+        sage: e0*e1
+        e1
+        sage: e0*e2
+        e2
+        sage: e0*e3
+        e3
+        sage: e1*e2
+        0
+        sage: e1*e3
+        0
+        sage: e2*e3
+        0
+
+    In one dimension, this is the reals under multiplication::
+
+      sage: J1 = eja_ln(1)
+      sage: J2 = eja_rn(1)
+      sage: J1 == J2
+      True
+
+    """
+    Qs = []
+    id_matrix = identity_matrix(field,dimension)
+    for i in xrange(dimension):
+        ei = id_matrix.column(i)
+        Qi = zero_matrix(field,dimension)
+        Qi.set_row(0, ei)
+        Qi.set_column(0, ei)
+        Qi += diagonal_matrix(dimension, [ei[0]]*dimension)
+        # The addition of the diagonal matrix adds an extra ei[0] in the
+        # upper-left corner of the matrix.
+        Qi[0,0] = Qi[0,0] * ~field(2)
+        Qs.append(Qi)
+
+    A = FiniteDimensionalAlgebra(QQ,Qs,assume_associative=True)
+    return JordanAlgebra(A)