eja: add inner_product() for DirectSumEJA.

[sage.d.git] / mjo / eja / eja_algebra.py

diff --git a/mjo/eja/eja_algebra.py b/mjo/eja/eja_algebra.py
index 3f91ee3ae72c6281c9238804f146944d2c431f1e..def2028a6a29a0d64733c8ed5c8a38e226c37f81 100644 (file)
--- a/mjo/eja/eja_algebra.py
+++ b/mjo/eja/eja_algebra.py
@@ -2399,3 +2399,83 @@ class DirectSumEJA(FiniteDimensionalEuclideanJordanAlgebra):
         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)
+
+    def inner_product(self, x, y):
+        r"""
+        The standard Cartesian inner-product.
+
+        We project ``x`` and ``y`` onto our factors, and add up the
+        inner-products from the subalgebras.
+
+        SETUP::
+
+
+            sage: from mjo.eja.eja_algebra import (HadamardEJA,
+            ....:                                  QuaternionHermitianEJA,
+            ....:                                  DirectSumEJA)
+
+        EXAMPLE::
+
+            sage: J1 = HadamardEJA(3)
+            sage: J2 = QuaternionHermitianEJA(2,QQ,normalize_basis=False)
+            sage: J = DirectSumEJA(J1,J2)
+            sage: x1 = J1.one()
+            sage: x2 = x1
+            sage: y1 = J2.one()
+            sage: y2 = y1
+            sage: x1.inner_product(x2)
+            3
+            sage: y1.inner_product(y2)
+            2
+            sage: J.one().inner_product(J.one())
+            5
+
+        """
+        (pi_left, pi_right) = self.projections()
+        x1 = pi_left(x)
+        x2 = pi_right(x)
+        y1 = pi_left(y)
+        y2 = pi_right(y)
+
+        return (x1.inner_product(y1) + x2.inner_product(y2))