X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Feja%2Feja_subalgebra.py;h=1286a167f4c5ede4fa45252a545fd848f3014ab9;hb=0d8b735dfd414a24c2d1f148c768f9362bb826b8;hp=68f1ce4cf8b5f07087e4474069ad4ebe5c6a4998;hpb=757cc5c671346394eff0a6de15c879598e508c61;p=sage.d.git

diff --git a/mjo/eja/eja_subalgebra.py b/mjo/eja/eja_subalgebra.py
index 68f1ce4..1286a16 100644
--- a/mjo/eja/eja_subalgebra.py
+++ b/mjo/eja/eja_subalgebra.py
@@ -15,7 +15,6 @@ class FiniteDimensionalEJASubalgebraElement(FiniteDimensionalEJAElement):
     The matrix representation of an element in the subalgebra is
     the same as its matrix representation in the superalgebra::
 
-        sage: set_random_seed()
         sage: x = random_eja(field=QQ,orthonormalize=False).random_element()
         sage: A = x.subalgebra_generated_by(orthonormalize=False)
         sage: y = A.random_element()
@@ -28,7 +27,6 @@ class FiniteDimensionalEJASubalgebraElement(FiniteDimensionalEJAElement):
     works like it does in the superalgebra, even if we orthonormalize
     our basis::
 
-        sage: set_random_seed()
         sage: x = random_eja(field=AA).random_element()
         sage: A = x.subalgebra_generated_by(orthonormalize=True)
         sage: y = A.random_element()
@@ -71,7 +69,6 @@ class FiniteDimensionalEJASubalgebraElement(FiniteDimensionalEJAElement):
 
         We can convert back and forth faithfully::
 
-            sage: set_random_seed()
             sage: J = random_eja(field=QQ, orthonormalize=False)
             sage: x = J.random_element()
             sage: A = x.subalgebra_generated_by(orthonormalize=False)
@@ -210,7 +207,17 @@ class FiniteDimensionalEJASubalgebra(FiniteDimensionalEJA):
 
         """
         if elt in self.superalgebra():
-            return super()._element_constructor_(elt.to_matrix())
+            # If the subalgebra is trivial, its _matrix_span will be empty
+            # but we still want to be able convert the superalgebra's zero()
+            # element into the subalgebra's zero() element. There's no great
+            # workaround for this because sage checks that your basis is
+            # linearly-independent everywhere, so we can't just give it a
+            # basis consisting of the zero element.
+            m = elt.to_matrix()
+            if self.is_trivial() and m.is_zero():
+                return self.zero()
+            else:
+                return super()._element_constructor_(m)
         else:
             return super()._element_constructor_(elt)
 
@@ -227,6 +234,10 @@ class FiniteDimensionalEJASubalgebra(FiniteDimensionalEJA):
         r"""
         Return the embedding from this subalgebra into the superalgebra.
 
+        SETUP::
+
+            sage: from mjo.eja.eja_algebra import HadamardEJA
+
         EXAMPLES::
 
             sage: J = HadamardEJA(4)