Overall, this exam was more difficult than Exam 1 and several of the
problems turned out to be quite challenging (actually, three of them
were impossible!).

The average scores by problem (as explained on the cover sheet, the
score for a good answer for each problem was 9, other than the Cover
where a “good” answer was worth 6 points) are:

By popular request, here are some practice problems for preparing to Exam 2: [PDF]

We won’t be providing written solutions to these problems, but are
happy to answer questions about them (including during office
hours). If you would like any particular problems to be included in
the review class (Monday), let us know.

The grades for PS4 are now posted in Assignments on Collab. You will find your grades, comments, and an attached pdf of solutions with PS2 assignment

Our grading policy for PS4 was the same as for PS1, PS2, and PS3, but we reserve the right to change this policy for future assignments.

To calculate your grade we first computed the following:

five_count = the count of problems for which you earned a 5 or above

sum = the sum of the scores earned on all problems

non_star_count = the number of non-starred problems in the assignent

score_by_fives = five_count / non_star_count

score_by_average = sum / non_star_count

That policy was:

You earned an A if score_by_fives >= 0.80 or score_by_average >= 4.5

You earned a B if score_by_fives >= 0.70 or score_by_average >= 4.0

You earned a C if score_by_fives >= 0.60 or score_by_average >= 3.5

You earned a D if score_by_fives >= 0.50 or score_by_average >= 3.0

Bonuses were added when we felt it appropriate.

If you did not receive a grade for the assignment, this is mostly likely because you submitted late, and we could find no record of us giving you permission to do so.

Exam 2 will be Wednesday, 6 November at the normal class time
in the normal classroom. We will aim to start the exam right at
3:30pm, so you will benefit from arriving early for class Wednesday to
be settled and ready to start the exam.

Exam 2 will cover material from Classes 1-16 (through 28 October) (so
the new material introduced on Rice’s Theorem in Class 17 is not
covered in this exam), Problem Sets 1-6 (comments for PS4 and PS5 are
now available in collab, sorry it has taken so long to get the grading
done for these, but you can see our solutions and comments in collab
now; we will post comments for Problem Set 6 on Sunday afternoon), and
the textbook chapters 0-6 and parts of 8 (8.1-8.4).

Most of the questions on the exam will cover topics that you will
have seen in at least two different places (e.g., both in class and on
a problem set, or in multiple classes, or at least both in the
textbook and in class or a problem set). The exam will emphasize
material that was not covered by Exam 1 (so focusing on the material
on problem sets 4-6), but will also build on material earlier in the
class, and you should be surprised if it does not include induction
proofs.

As a reminder from the syllabus, you may construct a one-page
(letter-size, two-sided) reference sheet for use during the exam,
but all other resources are forbidden (no internet, textbook, other
humans, magnification instruments, etc.). We expect that students will
benefit from thinking about what to put on your reference sheet in
preparing for the exam, and you may work with anyone you want
(including other students in the class) to prepare a reference sheets
together.

The class on Monday (November 4) will include an exam review. If you
have specific topics or problems you would like the review to cover,
slack them to @Dave.