CS 201: Tests

Test #1 will be given in-class on Friday, February 25. It will cover logic and proofs. Check the sample test.

The original of Test #1 is available in Postscript or PDF form. The solutions are also available in Postscript or PDF form.

Common problems on this test:

On the first problem, many of you mistakenly used (~z <-> y) as the negation of (z <-> ~y); in fact, the two are the same! The correct negation is simply (z <-> y) (which is the same as (~z <-> ~y)).
This problem was a killer! And I really did not mean it, honest, folks! If you look at the solution sheet, you'll see that the proof is very simple. The problem started when most of you ignored the big hint (the parenthetical sentence "note the two directions") and tried a single proof instead of the two proofs (one for each direction) needed in a "if and only if" situation. Several of you tried just one direction, confusing it with the whole thing; even the few who saw both directions and set up the problem properly forgot our technique of writing "divisible by k" as an arithmetic expression -- here writing n=19*i, where i is some integer. Not writing that is pretty much fatal -- there is no easy way to prove anything without that kind of very concrete evidence.
In contrast, most of you did OK on this one, although too many of you gave up on the simple algebra -- find the perseverance and patience somewhere in your soul! Mathematics and, even more so, computing are really about patience and perseverance, as well as about precision of thought and of expression.
Another troublemaker of a problem. Many of you appeared to have the right idea, but failed to express it properly. Welcome to program correctness ;-) Expressing what an imperative program does is not easy; for instance, note that the variable z at step k needs to be distinguished from the variable z at step k+1 -- mathematically, these are two entirely separate entities or, better, all of the incarnations of this variable form a function of the step number. Check the solution sheet to see how simple the solution is -- but pay particular attention to how you would express the relation in terms of the step number.

The grades went from 14.5 to 77.5 (on a scale of 0-100), with an average of 48.6 and a median of 50. I will schedule a "catch-up" test for those of you who want to improve their scores -- mechanism to be discussed in class on Monday. For now, you can interpret your scores roughly as follows: anyone with a score of 75 or better gets an A (2 people); scores from 65 to 74 earn a B (5 people); scores from 48 to 64 earn a C (8 people); scores from 24 to 47 earn a D (9 people); and scores below 24 get an F (3 people). But these scores will be modified for those of you who take the "catch-up" test.

The make-up for Test #1 will be given Friday, March 10. I will bring copies to class, but it will also be available on the web. Pick up the test at 8am (or any time thereafter on the web) and return your work to me by 5pm that same day -- you can slip your test under my door (EECE 236C), put it in my mailbox at the CS department, or email me your file.
Taking this test is optional, but recommended to everyone, even the two of you who earned an A on the first test: it cannot lower your score (I will not average, nor take the better of the two, but instead add to your original score as a function of your score on the make-up). It is not a test in the usual sense -- that is, the score you obtain on it is not an absolute result, but just an incremental one.
The test is open-book, open-notes; naturally, you may not speak about any of the questions to anyone except me -- contact me during the day by email (best), phone (75699), or by coming to my office (I have some errands to run this morning, but will be in all afternoon).
The make-up test for Test #1 is now available.

Test #2 will cover the material of Chapter 3 (minus the section on recurrences). A sample test is available here and a solution for it here.

The original of Test #2 is available in Postscript or PDF form. The solutions are also available in Postscript or PDF form. The grade distribution and a rough correspondence between numerical and letter grades is here.

The make-up for Test #2 is available here; it is due tomorrow morning, Friday 21, at 8am. As in the first make-up, this is not a regular test -- that is, it has problems of varied difficulty and is somewhat longer than a regular test, in order to give me a better idea of how well you understand and can work with this material.

Solutions for the make-up are available in Postscript and in PDF form.

Graded make-ups are in my box by my door (scores on it reflect a maximum regular score of 100; the highest score was a 92, obtained by two people). After reconciling your test grades and your make-up grades, I obtained the following compound grade distribution: 1 A+, 2 A, 1 A-, 3 B+, 1 B, 1 B-, 3 C+, 3 C, 2 D+, and 2 D.

Test #3 will cover relations and (di)graphs. It will be a take-home test, given on Thursday morning and due on Tuesday of finals week. There will not be a final.
You can get (in HTML) Test #3 and its solutions. A grade distribution and rough guide for scaling can be found here.

Final grades for the semester:

2 A
2 A-
1 B+
6 B
2 B-
2 C
3 C-
2 D

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