modify EV6 to sometimes use R^5 vectors

Author: StevenClontz

source/linear-algebra/exercises/outcomes/EV/EV6/generator.sage

@@ -3,10 +3,16 @@ TBIL.config_matrix_typesetting()
 
 class Generator(BaseGenerator):
     def data(self):
-        #Pick some  vectors in R4
-        n=choice([4,5])
+        #Choose R^4 or R^5, will use 5 or 4 vectors respectively
+        base_dim = choice([4,5])
+        vector_count = 9-base_dim
+        #answer will be 2 or 3
         dim=choice([2,3])
-        A=CheckIt.simple_random_matrix_of_rank(dim,columns=n,rows=4)
+        A=CheckIt.simple_random_matrix_of_rank(
+            dim,
+            columns=vector_count,
+            rows=base_dim
+        )
         basis=[A.column(i) for i in A.pivots()]
 
         return {