From: Michael Orlitzky <michael@orlitzky.com>
Date: Sun, 19 May 2024 01:50:53 +0000 (-0400)
Subject: mjo/cone/faces.py: use simpler dual face formula
X-Git-Url: http://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=03c7fb31b574c303acc413c81b8be8bbdd9aec09;p=sage.d.git

mjo/cone/faces.py: use simpler dual face formula
---

diff --git a/mjo/cone/faces.py b/mjo/cone/faces.py
index 6c5843e..0d9986d 100644
--- a/mjo/cone/faces.py
+++ b/mjo/cone/faces.py
@@ -207,9 +207,8 @@ def dual_face(K,F):
         True
 
     """
-    # Ensure that F is actually a face of K before continuing.
     if not F.is_face_of(K):
         raise ValueError("%s is not a face of %s" % (F,K))
 
-    span_F = Cone((c*g for c in [1,-1] for g in F), F.lattice())
-    return K.dual().intersection(span_F.dual())
+    # Hilgert, Hoffman, and Lawson Proposition I.1.9
+    return K.dual().intersection(-F.dual())