HW 7 comments

Max 6
Min 2.8
Mean 4.33
Median 4.4
 
Comments:
 
A.  A few do not realize that they need to consider all possible subsets if they use Hall's
theorem to prove the existence of an X-saturating matching.
 
B. Some considered X to be the collection of legislators and proved that there is no X-saturating
matching, which does not answer the question.
 
C. Quite a number of students know how to solve this, but they fail to state clearly what the vertex
set is, and when to join two vertices together.
 
D, E. Some fail to get the min cut in this case. Some students, instead of finding the cut starting
with a set S, just write down some collection of arcs. However, not every collection of arcs is a
cut.
 
F. Some students claim that k|N_A(U)|=k|U|, forgetting that there can exist arcs joining vertices
in N_A(U) to vertices in the complement of U in X.