hudebnik

I was supposed to be in front of a classroom half an hour ago. Instead, I'm still sitting on a train. But at least it's moving now, and I don't expect to be late for my next class.

Graphics class: drew a diagram of a pinhole camera, with an image appearing upside-down on the back wall. Replaced the box with an eyeball. Asked "why is the image upside-down? Why not flipped left-right, or something else? Why should the direction of up-or-down be privileged? Light rays aren't significantly affected by gravity (except near a black hole, which we aren't)."

Did some more thought experiments until one student said "it's not upside-down, it's rotated." So we discussed rotation, reflection, scaling, etc. and I promised that all that stuff they learned in Linear Algebra would actually make sense and be useful this semester.

Computer Architecture class: discussed units, and why E = mc^2 makes sense but E = mc^3 couldn't possibly have been right. Word problem: I walk at 2 steps/second, each step covering 2.5 feet. I jog at 3 steps/second, each step covering 4 feet. If I alternate jogging 75 steps with walking 75 steps, how fast am I moving on average?

Solved the problem two different plausible ways, getting different plausible answers. Discussed which one was wrong, and why. What happens if I lengthen my jogging stride to 5 feet? Obviously this is a 25% increase in jogging speed, but what's the percentage increase in average speed? What if instead of alternating every 75 steps, I alternated every 30 seconds, or every 100 yards? Good discussion.

Data structures class: let's explore a vague problem. In the game of SubDivvy, the players agree on a positive integer to start with, and on each turn, the current player chooses a proper divisor of the current number, subtracts it from the current number, and that becomes the new "current number." Tell me everything you can about the behavior of this game.

Then commenced a series of student-led discussion. Debated definition of "proper divisor"; agreed to exclude the current number itself (or the game end in one turn), and negatives (or the game goes forever). Not sure whether to exclude 1. Defined loss of game as "there is no proper divisor," which means the number is 1 (if we allow 1 as a proper divisor) or prime (if we don't). Proved that current number only decreases, never reaches 0, and never goes negative. Proved that in the allow-1 version of the game, game always ends after at most n-1 turns; still working on minimum number of turns. Proved that (still in the allow-1 version) 1 is a losing configuration, 2 is winning, 3 is losing, and 4 can be won or lost depending on what you choose as the first move -- in other words, strategy does matter in this game (there are games in which it doesn't). Wait: we've been assuming there are 2 players, which I never said. What if there were 3, or 4...? At the bell, left students with the challenge of characterizing winning and losing game states. Good discussion.

If only every day of classes went this way....

I attended a live-webcast-seminar on dealing with Asperger's syndrome at the college level. I went into it thinking "I have an unfair advantage, because Aspergerish behavior is almost normal in my field; what's to deal with?" But I figured there would be some useful tips for recognition, accommodation, and referral.

On recognition: one slide showed kids fighting with boffer swords and shields; another showed a table of the Klingon alphabet; another mentioned odd clothing "such as a cape, elaborate jewelry, scarves or embroidery"; D&D, WoW, LARP, and anime were mentioned by name, as were "odd interests" such as car motors, Victorian door hinges or vintage toys. The presenter hastened to point out that not ALL Aspergerians do these things, and some are offended by being lumped in with those people. Notable by its absence was any suggestion that not ALL people who do those things have Asperger's.

[I'm trying to think of people I know who don't do any of these things....]

On accommodation: six slides in a row on being clear, concise, and consistent. Each slide was illustrated with a "do" statement of 5-10 words, and a "don't" statement of 40-60 that said the same thing wrapped in a lot of qualifiers and softening particles. Seriously, would anybody prefer the latter? I guess this is the old tact-filter phenomenon again.

We're past the one-hour mark, I can't think of anything substantial I've learned yet, and I have to catch a train. I guess I'll have to skip the "referral" section.

On my feedback form I expressed a wish that the webinar itself had been more clear, concise, and consistent. :-)

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I walked into my 9:25 class prepared to talk about various Prolog topics: arithmetic (and the difference between "=" and "is"), modifying the rulebase to remember state information, and recursion. But before I could get started on that, a student needed some help with the Ruby assignment I gave him two weeks ago.

In the 10:50 class, I planned to contrast Java classes and C++ classes, pointing out both the syntactic gotchas and the real semantic differences. Got sidetracked into explaining some Java issues that the students hadn't learned last year (the subtleties of writing a correct "equals()" method, and the difference between overriding and overloading).

The 12:15 class is in Scheme: I was planning to introduce conditionals today, but as usual, nobody had read the assigned reading so we spent the period writing Boolean-valued functions. Some students basically got it, while others are still doing the deer-in-the-headlights, no-idea-where-to-start thing, no matter how many times I have them work through the exact same step-by-step recipe. I've been teaching this course for ten years, and have never had a class this weak: I've already lopped ten chapters off the thirty I was hoping to cover in a semester, and they're not keeping up with even that reduced pace.

The 1:40 class is the two-student tutorial. Nominally about computer graphics, which we're doing in OpenGL and C++, but the two students are working on final projects, one of which is a compiler from Hammer to OpenGL. I had pointed out to the student that if he's parsing configuration files, he should consider using lex and/or yacc, so I was helping him with those languages. He's considering doing the project not in C++/lex/yacc but rather in Java/JavaCC, so he showed me some JavaCC. Meanwhile, the other student took time out from his graphics homework to tell me about the Factor language, a sort of Forth-made-practical that he's researching for a class presentation.

Anyway, I'm outa here, catching a plane tonight to a conference. Which will be mostly in English :-)

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