From: Michael Orlitzky <michael@orlitzky.com>
Date: Fri, 2 Nov 2018 04:43:24 +0000 (-0400)
Subject: cone/faces.py: test that dual-face-of-dual-face is a no-op.
X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=064a3c7c3796f931954f8ece0b6e9912163efc1b;p=sage.d.git

cone/faces.py: test that dual-face-of-dual-face is a no-op.
---

diff --git a/mjo/cone/faces.py b/mjo/cone/faces.py
index ee16890..81b8421 100644
--- a/mjo/cone/faces.py
+++ b/mjo/cone/faces.py
@@ -202,6 +202,16 @@ def dual_face(K,F):
         sage: points_cone.dual().is_equivalent(dual_face(K, phi_y))
         True
 
+    Since all faces of a polyhedral cone are exposed, the dual face of a
+    dual face should be the original face [HilgertHofmannLawson]_::
+
+        sage: set_random_seed()
+        sage: def check_prop(K,F):
+        ....:     return dual_face(K.dual(), dual_face(K,F)).is_equivalent(F)
+        sage: K = random_cone(max_ambient_dim=8, max_rays=10)
+        sage: all([check_prop(K,F) for F in K.face_lattice()])
+        True
+
     """
     # Ensure that F is actually a face of K before continuing.
     if not F.is_face_of(K):