More minor tweaks to motzkin_decomposition().

diff --git a/mjo/cone/cone.py b/mjo/cone/cone.py
index eb5316330f6afefdc3b452482bfbd6d59deabbd2..28a84231d1eb461a1e12d0df258f980e48f21f2d 100644 (file)
--- a/mjo/cone/cone.py
+++ b/mjo/cone/cone.py
@@ -152,13 +152,15 @@ def motzkin_decomposition(K):
         sage: S.is_equivalent(expected_S)
         True
     """
-    # The lines() method only gives us one generator for each line,
-    # so we negate the result and combine everything for the full set.
-    S = Cone([p*l for p in [1,-1] for l in K.lines()], K.lattice())
+    # The lines() method only returns one generator per line. For a true
+    # line, we also need a generator pointing in the opposite direction.
+    S_gens = [ direction*gen for direction in [1,-1] for gen in K.lines() ]
+    S = Cone(S_gens, K.lattice())
 
     # Since ``S`` is a subspace, the rays of its dual generate its
     # orthogonal complement.
-    P = K.intersection( Cone(S.dual(), K.lattice()) )
+    S_perp = Cone(S.dual(), K.lattice())
+    P = K.intersection(S_perp)
 
     return (P,S)