CMPSCI 250: Introduction to Computation
David Mix Barrington
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
I generally answer my email fairly
TA Contact Info: Abhinav Parate,
firstname.lastname@example.org, office hours
Thursday 2:30-3:30, and Eric
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).
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)
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
out at the review session, which was taken almost verbatim from the
section of last term's CS250 website. I will
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
not all of them -- the graders still have around half. I will
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
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
- (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
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
- (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
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
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
- (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
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
- (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
- (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
In most respects the course will run like the Fall
2010 version of CMPSCI 250.
Last modified 19 May 2011