CAS CS 131  Fall 2018  Combinatoric Structures
Syllabus
Official Course Description
Representation, analysis, techniques, and principles for manipulation of
basic combinatoric data structures used in computer science. Rigorous
reasoning is emphasized. (Counts as a Background Course for the CS concentration.)
What this means in practice: we will train you in the mathematical foundations of CS so
that you can make convincing logical arguments (proofs) that programs you write and algorithms you
design are correct and run efficiently. The term "combinatorics" is centered on combinations
of objects belonging to a finite set  we will see applications in counting and probability
theory. For example, we will teach you things like how to compute the probability of randomly
guessing an alphanumeric password, or (similarly) how many Bitcoins you can expect to
mine with a given amount of computation.
Prerequisites: Basic (high school level) calculus and algebra.
Instructors and Teaching Fellows
Prof. John W. Byers
Homepage: http:// www.cs.bu.edu/fac/byers
Email: byers @ cs . bu . edu [preferred]
Office Hours: Tues 12:30  1:30PM (by prior appointment) and Thurs 1012 AM (open), in MCS 295B.
During office hours, if it's not too busy, I'll answer my phone at 6173538925.
Other times, I generally let phone calls go to voicemail. Please send email instead.
Prof. Charalampos (Babis) Tsourakakis
Homepage: https://tsourakakis.com
Email: tsourolampis @ gmail . com [preferred]
Office Hours: Thurs 56PM and Fri 1012AM in MCS 292.
Teaching Fellows: Konstantinos Ameranis, Anatoliy (Tolik) Zinovyev
Email: {ameranis, tolik} @ bu . edu
Office Hours, held in EMA 302 (or 303):

Konstantinos: Thurs 5  6PM, Friday 1  3PM.

Tolik: Wed 5:30  6:30PM, Friday 11AM1PM.
The class will be cotaught by Professors Byers and Tsourakakis. On any given lecture date, one of the two
instructors will deliver the lecture for both the A1 and B1 sections. One of the two TFs
will lead each of the discussion sessions. The objective is to reinforce the concepts covered in the lectures through
problemsolving, and to provide some clarifications and guidance on the homework assignments.
The purpose of the office hours of the Instructors and the Teaching Fellows is to answer specific
questions or clarify specific issues. Your fastest route to get an answer to
most questions is via Piazza. Office hours are not to be used to fill you in on a class you skipped or to
reexplain entire topics. Office hours are scheduled at times to provide help to students on the homework.
Office hours earlier in the week are invariably much less crowded.
Lectures
Lecture A1: Tues/Thurs 2  3:15 PM, CGS 129.
Lecture B1: Tues/Thurs 3:30  5 PM, CGS 129.
We expect students to come to class, and come on time.
While the class is large, class participation and questions will be encouraged.
Also, while our textbook will be very helpful, it is an imperfect substitute
for inclass learning, which is the fastest (and easiest) way to learn the material.
If you miss a class, please get the notes and work through the material from a
fellow student.
Discussion Labs
Lab A2: Wed 9:05  9:55AM, MCS B33
Lab A3: Wed 10:10  11AM, KCB 104
Lab A4: Wed 11:15  12:05PM, CAS B06B
Lab A5: Wed 12:20  1:10PM, MCS B23
Lab B2: Wed 1:25  2:15PM, CAS 235
Lab B3: Wed 2:30  3:20PM, WED 406
Lab B4: Wed 3:35  4:25PM MCS B23
Lab B5: Wed 4:40  5:30PM CAS 228
Labs will be an invaluable part of the course typically involving interactive
problemsolving sessions and further guidance on homework questions.
It is fine to sign up for A lecture and a B lab, or vice versa, as space permits.
Attendance is mandatory and will be taken.
Labs will not be held on Wed, September 5. The first section of lab will be held on Wed, September 12th.
Textbook
Discrete Mathematics and Its Applications, Kenneth H. Rosen, 8th Edition. ISBN 9781259676512
If you have access to another recent edition, that should be fine, although page numbers and
exercises will vary. It will be your responsibility to adjust accordingly.
Communications:
We will be using Piazza for class discussion.
The system is highly catered to getting you answers to your questions fast and
efficiently from classmates, the TFs, and the instructors.
Please do not email questions to the teaching staff  post your questions on Piazza instead.
We also encourage you to post answers to student questions there (but obviously, not
answers to problems on the problem sets!).
Our class page is located at:
https://piazza.com/bu/fall2018/cs131/home.
If you recently registered for the class, please go there to sign up today.
We will also use Piazza to post announcements and all handouts, including homework assignments and solutions.
Grading and Attendance
The course grade will break down as follows:
 Problem sets: 30%
 Midterms: 35%
 Final exam: 30%
 Lab attendance and participation in {lab, lecture, Piazza}: 5%
Last day to drop without a W: Oct 9. With a W: November 9. Our midterms are scheduled with these dates in mind.
Incompletes for this class will not be granted.
Exams:
There will be two inclass midterms held during the
middle of the semester, tentatively Thursday, October 4 and
Thursday, November 8.
The cumulative final will be held during the normal twohour final exam slot.
All exams will be in our regular lecture room, CGS 129.
The final exam matrix is *now finalized*, the same as the tentative times listed previously:
Tuesday, Dec 18, 35PM for students in the 2PM lecture
and Wednesday, Dec 19, 35PM for students in the 3:30PM lecture.
Please make your endofsemester travel plans accordingly!
Homework Assignments, Submission, and Late Policy:
Assignments will typically be due Fridays at 5PM.
You must submit electronically via Gradescope.
If you registered for the class after September 4, you will need to create a Gradescope
account and use entry code 9BB7ER to add CS131.
Plan on assignments being due every week, except right after a midterm,
tentatively Sep 14, Sep 21, Sep 28, Oct 12, Oct 19, Oct 26, Nov 2,
Nov 16, Nov 30, Dec 7.
Solutions will be posted at 5PM and homework assignments will NOT be accepted late.
Therefore, do NOT cut it close!! You may freely resubmit up to the deadline, so
we recommend you submit a preliminary version by 4PM.
To compute your homework grade, we will automatically drop the one
lowest score from the assignments, so one bad homework grade
is not the end of the world. However, we strongly recommend
putting forth your best effort on all assignments, as they
provide the best preparation for the exams.
As you likely already know, assignments requiring substantial creativity
can take more time than you expect, so plan to finish a day early.
Regrading Procedure:
If, after reviewing the posted solutions, you still believe a portion
of your homework was graded in error, you may request a regrade online via
Gradescope. Note that when we regrade a problem, your score may go up
or down.
Attendance:
It is expected that you will attend lecture and the
laboratory section for this course. Attendance will be taken in labs.
Often, some material covered in lecture and lab will not be covered by
our textbook. We ask that you please arrive to all classes on time,
since it is disruptive to have students flowing in throughout the class
period. When students are at a borderline between grades, we will
factor in attendance and participation before making a final determination.
Tentative Schedule (UPDATED LAST ON 11/27, probably the final update)
 Lecture  Topic  Readings  Homework Due Dates 
 9/4  Introduction to Proofs and Deductive Reasoning  Chapter 1.7  
 9/6  Propositional Logic  Chapter 1.11.2  
 9/11  Laws, logic circuits and satisfiability  Chapter 1.2  1.33  
 9/13  Predicates and quantifiers  Chapter 1.4  HW 1 due 9/14 
 9/18  Nested quantifiers  Chapter 1.5 (& skim 1.6)  
 9/20  Proof methods and techniques  Chapter 1.7  1.8  HW 2 due 9/21 
 9/25  More examples of proof techniques, sets  Chapter 2.1 (review)  
 9/27  Logic in Robotics. Sequences, Sets, Sums  Chapter 2.2 (review) and 2.4  HW 3 due 9/28 
 9/27  Intro to Induction  Chapter 5.1  
 10/4  Midterm 1, covers lectures through 9/28   
 10/9  No class (Columbus day turns Tuesday into a Monday)   
 10/11  Induction proofs  Chapter 5.1  HW 4 due 10/12 
 10/16  Strong induction  Chapter 5.2  
 10/18  Recurrences, recursive sets, structural induction  Chapter 5.3  HW 5 due 10/19 
 10/23  Recursive algorithms + division and GCD  Chapter 5.4, 4.3  
 10/25  Divisibility, numerical representations  Chapter 4.1, 4.2  HW 6 due 10/26 
 10/30  Extended GCD, solving congruences  Chapter 4.3  4.5 
 11/1  Primality, applications to crypto  Chapter 4.3  4.5  HW 7 due 11/2 
 11/6  BigO notation, algorithm runtime analysis  Chapter 3.2  3.3  
 11/8  Midterm 2, covers lectures through 11/1   
 11/13  Limits and bigO, analyzing recursive algorithms.  Chapter 3.3, 5.4  
 11/15  Divide and conquer algorithms, master theorem.
 Chapter 8.3  HW 8 due 11/16 
 11/20  Counting  Chapter 6.1, 6.2  
 11/22  No Class (Happy Thanksgiving!)   
 11/27  Counting  Chapter 6.2 (and 2.3.5), 6.3  
 11/29  Counting  Chapter 6.4  HW 9 due 11/30 
 12/4  Probability  Chapter 7.17.2  
 12/6  Probability  Chapter 7.2  HW 10 due 12/7 
 12/11  Probability  Chapter 7.3 

Academic Conduct
Academic standards and the code of academic conduct are taken very seriously
by our university, by the College of Arts and Sciences, and by the Department of
Computer Science. Course participants must adhere to the
CAS Academic
Conduct Code  please take the time to review this document if you are unfamiliar
with its contents.
Collaboration Policy
The collaboration policy for this class is as follows.
 You are encouraged to
collaborate with one another in studying the textbook and lecture material.
 As long as it satisfies the following conditions, collaboration on the homework assignments is permitted and will not reduce your grade:
 Before discussing each homework problem with anyone
else, you must give it an honest halfhour of serious thought.
 You may discuss ideas and approaches with other students in the class, but not share any
written solutions. In other words, the writeups you submit must be entirely your own work.
You must also acknowledge clearly in the appropriate portion of your solutions
(e.g., at the top of your writeups) people with whom you discussed ideas for that portion.
 You may get help from TFs for the class for specific problems in lab and at office hours.
 You may not work with people outside this class (but come and talk to us if you
have a tutor), seek online solutions, get someone else to do it for you, etc.
 You are not permitted to collaborate on exams.
The last point is particularly important: if you don't make an honest effort
on the homework but always get ideas from others, your exam scores (accounting
for the majority of your grade) will reflect it.