X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;ds=sidebyside;f=mjo%2Feja%2Feja_algebra.py;h=183e4cb978c233dbac31e321e855978309b27687;hb=a2cfe216f45da307ed6d1f75ffaa9d48565dc33e;hp=b9389da25e69722f04633c8324998d8d4834608a;hpb=5f522a9ac121a1229c0a9c62244b18ca67e65b12;p=sage.d.git

diff --git a/mjo/eja/eja_algebra.py b/mjo/eja/eja_algebra.py
index b9389da..183e4cb 100644
--- a/mjo/eja/eja_algebra.py
+++ b/mjo/eja/eja_algebra.py
@@ -2324,6 +2324,7 @@ class DirectSumEJA(FiniteDimensionalEuclideanJordanAlgebra):
 
     """
     def __init__(self, J1, J2, field=AA, **kwargs):
+        self._factors = (J1, J2)
         n1 = J1.dimension()
         n2 = J2.dimension()
         n = n1+n2
@@ -2345,3 +2346,97 @@ class DirectSumEJA(FiniteDimensionalEuclideanJordanAlgebra):
                                            check_axioms=False,
                                            **kwargs)
         self.rank.set_cache(J1.rank() + J2.rank())
+
+
+    def factors(self):
+        r"""
+        Return the pair of this algebra's factors.
+
+        SETUP::
+
+            sage: from mjo.eja.eja_algebra import (HadamardEJA,
+            ....:                                  JordanSpinEJA,
+            ....:                                  DirectSumEJA)
+
+        EXAMPLES::
+
+            sage: J1 = HadamardEJA(2,QQ)
+            sage: J2 = JordanSpinEJA(3,QQ)
+            sage: J = DirectSumEJA(J1,J2)
+            sage: J.factors()
+            (Euclidean Jordan algebra of dimension 2 over Rational Field,
+             Euclidean Jordan algebra of dimension 3 over Rational Field)
+
+        """
+        return self._factors
+
+    def projections(self):
+        r"""
+        Return a pair of projections onto this algebra's factors.
+
+        SETUP::
+
+            sage: from mjo.eja.eja_algebra import (JordanSpinEJA,
+            ....:                                  ComplexHermitianEJA,
+            ....:                                  DirectSumEJA)
+
+        EXAMPLES::
+
+            sage: J1 = JordanSpinEJA(2)
+            sage: J2 = ComplexHermitianEJA(2)
+            sage: J = DirectSumEJA(J1,J2)
+            sage: (pi_left, pi_right) = J.projections()
+            sage: J.one().to_vector()
+            (1, 0, 1, 0, 0, 1)
+            sage: pi_left(J.one()).to_vector()
+            (1, 0)
+            sage: pi_right(J.one()).to_vector()
+            (1, 0, 0, 1)
+
+        """
+        (J1,J2) = self.factors()
+        n = J1.dimension()
+        pi_left  = lambda x: J1.from_vector(x.to_vector()[:n])
+        pi_right = lambda x: J2.from_vector(x.to_vector()[n:])
+        return (pi_left, pi_right)
+
+    def inclusions(self):
+        r"""
+        Return the pair of inclusion maps from our factors into us.
+
+        SETUP::
+
+            sage: from mjo.eja.eja_algebra import (JordanSpinEJA,
+            ....:                                  RealSymmetricEJA,
+            ....:                                  DirectSumEJA)
+
+        EXAMPLES::
+
+            sage: J1 = JordanSpinEJA(3)
+            sage: J2 = RealSymmetricEJA(2)
+            sage: J = DirectSumEJA(J1,J2)
+            sage: (iota_left, iota_right) = J.inclusions()
+            sage: iota_left(J1.zero()) == J.zero()
+            True
+            sage: iota_right(J2.zero()) == J.zero()
+            True
+            sage: J1.one().to_vector()
+            (1, 0, 0)
+            sage: iota_left(J1.one()).to_vector()
+            (1, 0, 0, 0, 0, 0)
+            sage: J2.one().to_vector()
+            (1, 0, 1)
+            sage: iota_right(J2.one()).to_vector()
+            (0, 0, 0, 1, 0, 1)
+            sage: J.one().to_vector()
+            (1, 0, 0, 1, 0, 1)
+
+        """
+        (J1,J2) = self.factors()
+        n = J1.dimension()
+        V_basis = self.vector_space().basis()
+        I1 = matrix.column(self.base_ring(), V_basis[:n])
+        I2 = matrix.column(self.base_ring(), V_basis[n:])
+        iota_left = lambda x: self.from_vector(I1*x.to_vector())
+        iota_right = lambda x: self.from_vector(I2*+x.to_vector())
+        return (iota_left, iota_right)