This is the home page for CMPSCI 250. CMPSCI 250 is the undergraduate core course in discrete mathematics and will deal with logic, elementary number theory, proof by induction, recursion on trees, search algorithms, finite state machines, and a bit of computability.

**Instructor Contact Info:**
David Mix Barrington, 210 CMPSCI
building, 545-4329, office hours Tuesday 2-4, Wednesday 2:30-3:30, and
Friday 2:30-3:30.
I generally answer my email fairly
reliably.

**TA Contact Info:** Abhinav Parate,
aparate@cs.umass.edu, office hours
Thursday 2:30-3:30, and Eric
Ssebanakitta, essebana@cs.umass.edu,
office hours Monday 1-2. TA office hours are in LGRT 220.

The course is primarily intended for undergraduates in computer science and related majors such as mathematics or computer engineering. CMPSCI 187 (programming with data structures) and MATH 132 (Calculus II) are corequisites and in fact most students in the course have already taken both.

The course meets for three lecture meetings a week, Monday, Wednesday,
and Friday, at 11:15-12:05, in Lederle *Tower* ("LGRT") room 101.

There is one discussion meeting per week, meeting on Fridays 10:10-11:00. The students have been arbitrarily divided into two discussion sections. Section 01 meets in ELAB 323, and Section 02 meets in room 142 of the Computer Science Building. Most discussions will have a written assignment which you will carry out in groups, chosen randomly at the beginning of each discussion. Discussion attendance is required, so that missing a discussion will incur a grade penalty. The TA and I will probably alternate which sections we lead, so they should be as interchangeable as we can make them.

The textbook is several chapters of my draft version of
*Discrete Mathematics: A Foundation for Computer Science*. Photocopies
of this will be available before the start of term,
probably for $53 (two volumes), at
Collective Copies in downtown
Amherst -- ask for course packet #19.
(Dave gets none of this money -- it is the
copying cost only.) If you have a copy of the CMPSCI 250 text for Fall 2010,
you should be able to use it, but pay attention to the corrections I have made in the new version (these were updated
during the break).

- Course Requirements and Grading
- Homework Assignment Directory (with HW#9)
- Discussion Assignment Directory (none so far)
- Exam Directory (with final exam and solution)
- Questions and Answers on Homework (with some on #9)
- Syllabus
- Errata in the (new) Textbook

**Announcements (19 May 2011):**

- (19 May) I have posted the final exam and its solution. You may pick up your graded exams this summer or fall from my office. Thanks for an enjoyable course!
- (18 May) I have finished the grading and posted the grades
on SPIRE, where you are apparently able to see them. I'll post the
aggregate statistics here now, and post the exam and solution (I hope)
by tonight.
I set the exam scale at A = 98, B = 80, C = 63, D = 45, F = 28. Exam scores were:

- A+ (8): 117, 116, 114, 109, 105, 105, 104, 101
- A (2): 96, 96
- A- (4): 95, 94, 93, 93
- B+ (4): 86, 86, 85, 84
- B (4): 82, 82, 80, 78
- B- (3): 77, 76, 73
- C+ (9): 71, 71, 70, 70, 69, 68, 68, 67, 66
- C (2): 63, 62
- C- (13): 60, 59, 59, 58, 58, 58, 57, 57, 57, 57, 56, 55, 55
- D+ (4): 54, 54, 53, 51
- D (2): 48, 43
- F (6): 42, 39, 37, 36, 22, 18

It is not good that 40% of the class was below C, but fortunately most of people with the C- exams, at least, were able to pass based on earlier work. It turns out that 22 of the 61 students that took the final benefited from counting the final at 50% rather than 25%. Here is the distribution of overall grades:

- A+ (in SPIRE as A, course citation will be filed): 5
- A: 3
- A-: 7
- B+: 6
- B: 5
- B-: 7
- C+: 14
- C: 7
- C-: 7
- D+: 1

The C- and D+ people get graduation credits, but will have to repeat 250 in order to take any later course that has it as a prerequisite. (We kick people out of courses they have already registered for if necessary.) None of those xweight people had C or better on the final, and only one had C or better on the homework, so I don't see much room for negotiation about this.

- (8 May) Here is the study guide I handed out at the review session, which was taken almost verbatim from the blog section of last term's CS250 website. I will hold office hours tomorrow (Monday) from 2-4 p.m., in my office.
- (4 May) I've received the rest of the graded HW#8's from the graders and I will have them available in office hours today and at the review session Friday. I don't yet have HW#9 solutions but I will post here when I do.
- (3 May) I don't yet have the remaining HW#8's but I hope to get them
tomorrow. I will hold my normal office hours tomorrow 2:30-3:30 --
*if*I have those homewworks and/or HW#9 solutions available by then I will post here saying so. - (2 May) When I handed back graded HW#8's this morning, it was not all of them -- the graders still have around half. I will announce here when I have the others to give back -- I may get them in time for my office hours 2-4 tomorrow.
- (2 May) I will hold a review session for the final exam in room 142 of the CMPSCI building, this Friday from 2:00-4:00. The final will be cumulative, with 50% on the last third of the course and 25% each on the first third and second third. It will probably be a bit longer than the midterms -- last year's final is a good model.
- (26 Apr) I have posted another q&a on HW#9, which corrects an error in the book on Writing Exercise 2 of Excursion 14.9.
- (25 Apr) I have posted the first question and answer on HW#9.
- (21 Apr) The last homework assignment is now posted.
- (21 Apr) Sorry they are so late, but I have just posted three questions and answers on HW#8, including a clarification to the extra credit question that makes it potentially worth fifteen points instead of ten. I'll post the HW#9 assignment, due at 4:00 p.m. on the last day of classes, later tonight. I will be away with very limited email access the whole weekend, and have to leave my office hours today at 3:30 or even a little before.
- (14 Apr) I have posted the HW#8 assignment, due a week from tomorrow. Nearly all of it is on material we will have covered by tomorrow, which is good since there is no lecture Monday. I think the problems are a bit shorter than the average has been.
- (10 Apr) Here are the results from the second midterm:
- A+ (103-110) 9 -- three 110's
- A (98-102) 9
- A- (92-97) 3
- B+ (87-91) 7
- B (82-86) 6
- B- (76-81) 9
- C+ (71-75) 8
- C (66-70) 3
- C- (60-65) 5
- D+ (55-59) 0
- D (50-54) 1
- F (0-49) 1, a 46

- (9 Apr) I have posted the second midterm and its solution. The scale will be A = 100, B = 84, C = 68, D = 52 -- I will post the aggregate results when I finish the grading, and that will be in time for me to hand back graded exams on Monday.
- (5 Apr) I have posted the HW#7 assignment, due a week from Friday. The HW index page now also has the planned due dates for HW#8 and HW#9.
- (3 Apr) I've been asked exactly which sections of the book
are covered on the test. For the most part this is answered by the
syllabus, which has a section or
sections for each lecture. So 4.8 and 4.10 are not on the syllabus
and thus not fair game for the test. We had no homework on 4.9 as
such, but this lecture was covered along with 9.1, with which it
overlaps material. Finally, the last subsection of 9.10, on
alpha-beta pruning, is not covered on the test because we did not
get to it in lecture.
As you can see from previous tests, the material from the first part of the course (Chapters 1, 2, and 3) may come up tangentially. For example, the tiling question on last fall's exam referred to modular arithmetic, and you might need the four quantifier proof rules in any situation where you are proving a quantified statement and you can't do it by induction.

- (2 Apr) I have restored the solutions to the second midterm of Fall 2007.
- (2 Apr) Here is the review of prior midterms I promised. In
Fall 2010, the second midterm was on pretty much the same material
as for this course, so any of those questions are fair game. In
Fall 2007, the second midterm would all be fair game except that
Question 3 is all number theory and would thus have been on our
first midterm, and Question 4 relies a bit too much on induction on
paths in a graph, which we haven't done that much. (Though that
directed graph should be very familiar by now!). (At the moment,
there are no solutions posted for the second Fall 2007 midterm
because they were lost in a text-editing accident some time ago. If
I have time tonight I will write up new solutions.) The practice third
midterm for Fall 2007 is relevant except for Question 3, which is on
material that has since moved into CMPSCI 240. The real third
midterm for Fall 2007 would be ok except for Question 5 which is on
that same 240 material. (I threatened you with Question 1 on that
exam.)
In the earlier offerings of CMPSCI 250 on the web site, Fall 2004, Spring 2005, and Spring 2006, you should look primarily at the second midterms, which are mostly on induction. For the Fall 2004 practice test, look at questions 2, 4, 5, and 6. For the real second midterm of Fall 2004, look at questions 1, 3, 4, and 5. For the second midterm of Spring 2005, look at questions 1 and 2. For the second midterm of Spring 2006, look at questions 1, 2, and 3 (though 3 uses more string induction that we have done).

- (30 Mar) I have just posted a bunch of questions and answers on HW#6. I will add to this file as I get new questions, probably through tomorrow night.
- (30 Mar) There is an error in the textbook, messing up one of the crucial definitions of Section 9.9 -- check the errata page for details.
- (22 Mar) I have posted the HW#6 assignment, due a week from Friday, 1 April (no fooling). There are also some questions and answers on HW#5, which is due tomorrow.
- (6 Mar) I have posted the HW#5 assignment, to be due Wednesday 23 March, after the break.
- (4 Mar) I just posted a question and answer on HW#4. I'll be reading email for most of the weekend, and I will post other interesting questions and answers if I get them soon enough.
- (28 Feb) I have finished the grading and posted both the midterm and its solution. The scale for the midterm is A = 96, B = 80, C = 64, D = 48. The high was 109 and the low was 48, overall there were 9 A+'s, 4 A's, 5 A-'s, 3 B+'s, 8 B's, 11 B-'s, 10 C+'s, 7 C's, 7 C-'s, 1 D+, and 1 D. I'll hand back the exams tomorrow morning.
- (24 Feb) I am posting the HW#4 assignment tonight, due Monday 7 March. HW#5 will be due the Wednesday after spring break, 23 March, and HW#6 will be due Friday 1 April (no fooling), so that you can have solutions before the exam on Monday evening, 4 April.
- (24 Feb) I will post the exam and its solution over the weekend, as one student is going to take it tomorrow. I may have the grading finished by Monday, but Wednesday is more likely.
- (20 Feb) I mentioned in class several times that the exams from my previous offerings of CMPSCI 250 are good indications of what to expect on the forthcoming exam. I should clarify this a bit -- this exam covers the parts of Chapters 1, 2, and 3 listed on the syllabus, including 3.6 which we will cover on Tuesday. The first exam from Fall 2010 doesn't have much on number theory because we did much less of it that term. The first exams from Fall 2004, Spring 2005, Spring 2006, and Fall 2007 also don't have much number theory on them, because in those terms I divided the course into quarters rather than thirds, and thus number theory fell into the second quarter. You should thus look at the second midterms for those terms -- in particular Question 3 from Fall 2007, Question 2 from Spring 2006, Question 3 from Spring 2005, Questions 2 and 4 from Fall 2004, and Question 3 from the the practice exam from Fall 2004 are the sort of number theory questions I might ask. The length and difficulty of the exams are reasonably consistent across terms, so because I am asking more number theory I will ask a little less logic.
- (20 Feb) Remember that we have class on Tuesday at the normal time. On Wednesday at the normal time I will be in LGRT 101 to answer questions but there will be no new material. The exam is 7-9 p.m. Wednesday in ESCS 119.
- (11 Feb) I have posted the HW#3 assignment, due a week from Tuesday (which has a Monday schedule).
- (10 Feb) As I emailed to everyone, I am offering an optional extension until Monday morning at 11:15 for HW#2. But there is a cost -- if you hand it in on Monday I will deduct one letter grade (e.g., from a B to a C). To get full credit you must hand in your paper tomorrow in lecture.
- (8 Feb) I have posted some questions and answers on the second homework.
- (8 Feb) I've looked at the grades for HW#1 -- the high was 62, the only grade in the 60's. There were 16 in the 50's, 21 in the 40's, 20 in the 30's, and 11 below 30. The mean was 41.3. The people below 30 should be worried. The scale will be A = 54, B = 43.5, C = 33, D = 22.5, F = 12.
- (30 Jan) I have just posted the second homework assignment, due a week from Friday.
- (24 Jan) I have posted the first questions and answers on HW#1, a couple of errata in the new textbook, and the TA office hours (above).
- (20 Jan) There is snow forecast for tomorrow morning -- it is easy to find out the opening status of the University. We will have discussion classes if it is open by 10:10, and will have lecture class if it is open by 11:15.
- (20 Jan) I have posted the first homework assignment, due a week from Monday.
- (19 Jan) The textbooks are ready at Collective Copies -- I have updated the information above. Also, I have set my office hours and added the contact information for our two TA's, Abhinav and Eric. By a narrow vote, you chose to have most HW assignments due on Mondays, so the first homework will be posted soon and due on Monday 31 January. We won't grade it before the add/drop date, but we will hand out solutions in class and you should be able to judge your performance somewhat.
- (13 Jan) I have posted the syllabus and the requirements and grading page.
- (29 Dec) Enrollment for the course is currently closed. (SPIRE is currently showing a capacity of zero for technical reasons that I don't fully understand, but the planned capacity is about 72.) If you are already on the (department) waiting list for the course, we will be in touch. If you would like to be in the course but have not contacted us yet, please email email Darlene Fahey, the CMPSCI undergrad administrator, and let her know -- we will see what we can do. Since the course is oversubscribed, we cannot be very flexible with prerequisites.
- (29 Dec) Welcome to the preliminary version of the web site for CMPSCI 250 for Spring 2011. I am setting up the bare bones of the web site today. This section of the CMPSCI 250 main page will be essentially a blog of course announcements. In most respects the course will run like the Fall 2010 version of CMPSCI 250.

Last modified 19 May 2011