Trac 13158: local components bug finding minimal twist

sagemath · Jun 10, 2015 · 1994692 · 1994692
1 parent 336ae6c
commit 1994692
Showing 1 changed file with 13 additions and 2 deletions.
diff --git a/src/sage/modular/local_comp/type_space.py b/src/sage/modular/local_comp/type_space.py
@@ -364,6 +364,16 @@ def minimal_twist(self):
             14
             sage: TypeSpace(g, 7).is_minimal()
             True
+
+        Test that :trac:`13158` is fixed::
+
+            sage: from sage.modular.local_comp.type_space import TypeSpace
+            sage: f=Newforms(256,names='a')[0]
+            sage: T=TypeSpace(f,2)
+            sage: g = T.minimal_twist(); g
+            q - a*q^3 + O(q^6)
+            sage: g.level()
+            64
         """
         if self.is_minimal():
             raise ValueError( "Form is already minimal" )
@@ -382,8 +392,9 @@ def minimal_twist(self):
             V = A.submodule(VV, check=False)
 
         D = V.decomposition()[0]
-        if len(D.star_eigenvalues()) == 1:
-            D._set_sign(D.star_eigenvalues()[0])
+        if len(D.star_eigenvalues()) == 2:
+            D = D.sign_submodule(1)
+        D._set_sign(D.star_eigenvalues()[0])
         M = ModularForms(D.group(), D.weight())
         ff = Newform(M, D, names='a')
         return ff