eja: remove one use of nontrivial=True passed to random_eja().

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

diff --git a/mjo/eja/eja_element.py b/mjo/eja/eja_element.py
index 1cf93cce6127b476796cdc130bfd98cfb7f21e41..cf213a7a0f85d2e6eeb0edb13cba14b2bd8a49d6 100644 (file)
--- a/mjo/eja/eja_element.py
+++ b/mjo/eja/eja_element.py
@@ -346,6 +346,7 @@ class FiniteDimensionalEuclideanJordanAlgebraElement(IndexedFreeModuleElement):
         SETUP::
 
             sage: from mjo.eja.eja_algebra import (JordanSpinEJA,
+            ....:                                  TrivialEJA,
             ....:                                  random_eja)
 
         EXAMPLES::
@@ -364,6 +365,17 @@ class FiniteDimensionalEuclideanJordanAlgebraElement(IndexedFreeModuleElement):
             sage: x.det()
             -1
 
+        The determinant of the sole element in the rank-zero trivial
+        algebra is ``1``, by three paths of reasoning. First, its
+        characteristic polynomial is a constant ``1``, so the constant
+        term in that polynomial is ``1``. Second, the characteristic
+        polynomial evaluated at zero is again ``1``. And finally, the
+        (empty) product of its eigenvalues is likewise just unity::
+
+            sage: J = TrivialEJA()
+            sage: J.zero().det()
+            1
+
         TESTS:
 
         An element is invertible if and only if its determinant is
@@ -382,15 +394,21 @@ class FiniteDimensionalEuclideanJordanAlgebraElement(IndexedFreeModuleElement):
             sage: x,y = J.random_elements(2)
             sage: (x*y).det() == x.det()*y.det()
             True
-
         """
         P = self.parent()
         r = P.rank()
-        p = P._charpoly_coeff(0)
-        # The _charpoly_coeff function already adds the factor of
-        # -1 to ensure that _charpoly_coeff(0) is really what
-        # appears in front of t^{0} in the charpoly. However,
-        # we want (-1)^r times THAT for the determinant.
+
+        if r == 0:
+            # Special case, since we don't get the a0=1
+            # coefficient when the rank of the algebra
+            # is zero.
+            return P.base_ring().one()
+
+        p = P._charpoly_coefficients()[0]
+        # The _charpoly_coeff function already adds the factor of -1
+        # to ensure that _charpoly_coefficients()[0] is really what
+        # appears in front of t^{0} in the charpoly. However, we want
+        # (-1)^r times THAT for the determinant.
         return ((-1)**r)*p(*self.to_vector())
 
 
@@ -1220,6 +1238,17 @@ class FiniteDimensionalEuclideanJordanAlgebraElement(IndexedFreeModuleElement):
             sage: l0*c0 + l1*c1 == x
             True
 
+        The spectral decomposition should work in subalgebras, too::
+
+            sage: J = RealSymmetricEJA(4)
+            sage: (e0, e1, e2, e3, e4, e5, e6, e7, e8, e9) = J.gens()
+            sage: A = 2*e5 - 2*e8
+            sage: (lambda1, c1) = A.spectral_decomposition()[1]
+            sage: (J0, J5, J1) = J.peirce_decomposition(c1)
+            sage: (f0, f1, f2) = J1.gens()
+            sage: f0.spectral_decomposition()
+            [(0, 1.000000000000000?*f2), (1, 1.000000000000000?*f0)]
+
         """
         A = self.subalgebra_generated_by(orthonormalize_basis=True)
         result = []
@@ -1289,12 +1318,13 @@ class FiniteDimensionalEuclideanJordanAlgebraElement(IndexedFreeModuleElement):
         TESTS:
 
         Ensure that we can find an idempotent in a non-trivial algebra
-        where there are non-nilpotent elements::
+        where there are non-nilpotent elements, or that we get the dumb
+        solution in the trivial algebra::
 
             sage: set_random_seed()
-            sage: J = random_eja(nontrivial=True)
+            sage: J = random_eja()
             sage: x = J.random_element()
-            sage: while x.is_nilpotent():
+            sage: while x.is_nilpotent() and not J.is_trivial():
             ....:     x = J.random_element()
             sage: c = x.subalgebra_idempotent()
             sage: c^2 == c
@@ -1389,7 +1419,7 @@ class FiniteDimensionalEuclideanJordanAlgebraElement(IndexedFreeModuleElement):
             # the trace is an empty sum.
             return P.base_ring().zero()
 
-        p = P._charpoly_coeff(r-1)
+        p = P._charpoly_coefficients()[r-1]
         # The _charpoly_coeff function already adds the factor of
         # -1 to ensure that _charpoly_coeff(r-1) is really what
         # appears in front of t^{r-1} in the charpoly. However,