Math 3134, Applied Combinatorics and Graph Theory
(10:10-11:00 AM MWF, Derring 3092)


Final grades: The grades are posted here.  Many of you did a good job on the final.  There were a few surprises in both directions. As I promised, those that scored in the A range on the final (64-70 for an A, 55-63 for an A-) received that grade regardless of their past performance.  I will be out of town till the end of May.  You can stop by my office to look at your exam after that, but you should e-mail me first.  I spend less time there during the summer.  I plane to post solutions to the final exam eventually, check back later.

Syllabus: Check the syllabus for office hours, locations, and general advice on how to do well in the course. Or here is a pdf version to print.

Dijkstra's algorithm:

Exam solutions:
Homework assignments:

Remember that you must justify all your answers.

Assigned
Due
Read
Do but don't turn in
Do and turn in

On your own
You may discuss
1/17
1/24
1.1-4, 2.1-7, 3.1
2.1.33, 37, 39,
2.2.3, 6, 9, 23,
2.3.17, 27, 33,
2.4.1, 3, 7,
3.1.5, 7, 25

3.1.24
1/19
1/24 3.2
2.5.49, 51, 52, 63, 65, 67, 69,
2.6.7, 9, 13, 19, 29,
2.7.29, 41,
3.1.27-31, 35-37
3.1.38, 54
Bonus exercise: 2.7.47

1/21
1/24 3.2
3.1.42, 43
Exercise on directed graphs

3.1.41
1/24
1/31 3.2
3.2.9, 10, 48, 50-52, 58, 59
Note there is a mistake in 52, the top 2 vertices shouldn't be adjacent.

3.2.57
1/26
1/31 2.2, 2.5
2.2.4, 5, 7, 8, 10, 23,
2.5.64, 66, 68, 70
2.2.26, 31

1/28
1/31 2.2, 2.3, 3.2
2.2.11-13, 15, 17, 18,
2.3.51,
3.2.56

Graph isomorphism exercise
1/31
2/7
3.2
2.2.1, 2, 16, 19, 20 21, 24, 27, 28, 29
2.2.22
2.2.33 (Hint)
2/2
2/7
3.2
3.2.47, 48, 64
Exercise on paths and isomorphism

2/4
2/7
3.2
3.2.30-38, 53, 65
3.2.47

2/7
2/14
3.3
3.2.24, 26, 28, 30-38
Exercise on Euler circuits
(Further hints)

2/9
2/14
3.3
3.2.18, 20, 22, 39-41, 49, 54
3.2.41.c and d (make sure  to justify your answer)
3.2.61
2/11
2/14
3.3
3.2.42, 60, 63
3.2.47
Bonus exercise

2/14-18

3.3
No new exercises this week.  Prepare for exam.
2/21
3/2
3.4
3.3.1, 3, 5, 7, 11, 23, 24

3.3.21, 22
2/23
3/2
3.4
3.3.15, 17, 18

Correction to 3.3.23,
3.3.24
2/25
3/2
3.4, 3.5
3.3.1, 3, 9, 10, 20, 30, 31
Understand what the Maple worksheet on Dijkstra's algorithm does.


2/28
3/2
3.5
3.4.11, 13, 15, 16, 21, 29, 33, 37


3/2
3/14
4.1
3.5.38, 41, 42, 44, 45, 60
3.4.33
3.4.37
3/4
3/14
4.1
3.5.53, 57, 58, 68 (use Dijkstra's algorithm), 73, 80.
Understand the solutions to HW 5.


3/14-18

4.1, 4.2
No new exercises this week.  Prepare for exam.
3/21
3/28
4.1, 4.2
4.1.14, 16-18, 20, 46

Exercise (c) => (a) in Theorem 4.5
3/23
3/28
4.2
4.1.29, 31, 33-37, 45 (Hint: Remove any edge and use the inductive hypothesis on the resulting connected components.)
4.1.32, but also verify your answer by reconstructing the tree from the connection list. Do you get the original tree back?
Exercise (e) => (a) in Theorem 4.5
3/25
3/28
4.2
4.2.3, 9-13
No new HW to turn in. Enjoy the weekend.
3/28
4/4
4.2, 5.1
4.2.17, 19, 21, 23, 29, 31, 34, 37, 38, 40
4.2.32 (Make sure you justify your answer. If you are clever, you can save yourself a lot of work by using the fact that the original Prim's algorithm finds a minimal spanning tree.)
4.1.45 (Hint: We proved in class without using Theorem 4.3 that removing an edge from a tree disconnects it. So remove an edge and use the inductive hypothesis on the connected components.)
3/30
4/4
5.1, 5.2
4.2.42 (Hint: First prove that the graph given by Kruskal's algorithm is connected, hence it is a spanning tree. Now use the same idea as in our proof of Prim's algorithm to prove that its total weight must be minimal.)
4.2.45


4/1
4/4
5.2
5.1.1, 7, 11, 15, 17-19, 21, 26, 29
5.2.7, 29, 30, 31 (Do 31 first. It's easy. Now 29 and 30 are obvious consequences if you look at Theorem 3.8)
Bonus exercise: Find the mistake in the April's Fool proof I gave this morning. (If you were not in class, get someone's notes.)
5.1.23 (deadline extended to 4/11)
4/4
4/11
6.1
5.2.9, 17, 19
5.2.33
5.1.23 (New hint: find a set of distinct reps and compare its elements with the union of all sets)
4/6
4/11
6.1, 6.2
6.1.1-6, 7, 9, 11, 31


4/8
4/11
6.1, 6.2
6.1.19, 21, 23, 33, 35
Find a flow of value 0 for the network in Exercise 6.1.9, which is not 0 on every edge.
Let N be a network which has no cycles. Prove that the only flow of value 0 is the 0 flow (the flow that is 0 on every edge). (Hint: Look for a longest one among paths all of whose edges have nonzero flow.)
4/11-15

6.2
No new exercises this week.  Prepare for exam.
4/20
4/25
6.3, 6.4
6.2.1, 3, 11, 19, 23, 25
6.3.5, 9, 11
6.3.12, but find both a maximal flow and a minimal cut.
6.3.17

4/22
4/25
6.4, 7.1
6.3.7, 13, 14, 24 (We did this in class), 25

6.3.15 (Hint: Do (c) before (b).)
4/25
5/4
6.4, 7.1
6.4.7 (the network associated with a bipartite graph is the network we constructed in class by orienting the edges and adding a source and a sink), 9, 11, 13

6.4.29 (Hint: proof by contradiction. This is true anytime, not only in the last iteration.)

6.4.30 (Hint: Are there any labeled vertices that are not scanned if the algorithm ends with the sink unlabeled?)
6.4.12

4/27
5/4
7.1-4
6.4.31 (Hint: Notice that if X in V1 is labeled then there can be no edge with nonzero slack from X to an unlabeled vertex Y in V2 in the last iteration of the algorithm.)

7.1.1, 3, 19, 21, 23, 29, 30
7.1.37 (Hint: If the first integer is k, look at C(n+k-1,n) and give it a combinatorial interpretation.)
6.3.15 again, but use the worksheet.
4/29
5/4
7.2-4, 6
7.1.15-17, 25,

7.1.31 (Hint: Use C(n,k)=C(n-1,k)+C(n-1,k-1) repeatedly.),

7.1.35 (Hint: Use the Canadian lumberjack method to show C(n,k+1)-C(n,k) is nonnegative.),

7.1.38 (Hint: Differentiate x(x+1)^n once without expanding it first and once after expanding it using the Binomial Theorem. Now evaluate at x=1.),

7.2.11, 13, 15-17, 29, 31, 33, 34

7.1.33 (Hint: Use the result of 7.1.25 and C(n,k)=C(n,n-k).)
5/2
5/4
7.6
7.2.1, 5, 7,
7.3.15, 17, 24, 25, 27, 33,

7.4.1, 7, 9, 13, 19, 23, 24, 30, 31 (Hint: Notice that if you were to pick 3 out of the numbers 1 thru 10 with repetition allowed, you could always list them in decreasing order.),

7.4.36 (Hint: You could pick the t+1-st element 0 times, 1 time, 2 times, etc.),

7.6.1, 3

7.6.12 (Hint: Look at how many sequences of 5 integers contain no 4s, how many contain no 7s, and how many contain no 4s and 7s. The answer is 14670, but you need to justify it.)

You don't have to do the bonus exercises, but if you do it, you can score more than 100% on the HW.

Definition: Let X be a student in Math 3134. We say X understands a mathematical argument if X is able to reproduce that argument in writing on their own.