Evaluations

The STACS program committee meeting has ended. We have a couple of days to digest the results before they get sent out to authors. The way in which the committee virtual meeting was run was an impressive case of efficiency. We were given internal deadlines that we were actually supposed to respect, with no slack. That was stressful!

The life of a professor is very much driven by deadlines. The next item: recommendation letters that need to be written and sent out, many of them before December 1. A few days later, several referee reports are due. Then, wrapping up the semester's courses and deciding on final grades. Some of the intervals in between will be filled by attempts to bring my mailbox under control.

So much of our lives is occupied by evaluations. It is rather striking considering that that is neither teaching nor research proper.

Voting

When I voted in the village in France where I used to live, we did it the old-fashioned way: go in an isolated space whose privacy is protected by curtains, put a paper ballotin a small envelope, and drop it in the glass bin. On several occasions I volunteered to help count.

That Sunday evening (voting in France is always on Sundays), the volunteers gather, and we form 3 tables of four actors. The other people present are just watching the counting as it happens, to help guarantee its integrity.

The chair of the meeting unlocks the glass bin and envelopes are gathered in packets of one hundred. Our table gets a few of those packets. For each envelope, I open it, take out the bulletin and pass it to the person across the table from me. He looks at the name written on the ballot and reads it aloud. The two other persons, who each have a sheet of paper, record the vote. After each packet, they compare their tally and we check that the total sum is correct.

It's a mesmerizing procedure. Extremely easy, but we have to stay focused. By myself, I would perhaps make one or two mistakes in the 600 votes that my table counts. With the four of us controlling the process (plus onlookers), the rare mistakes get noticed right away. Everyone is focused: we're all conscious of the importance of the act. Democracy in action! I am also fascinated by the tallies, trying to predict who will win, looking for patterns and trying to explain them. Overall, voting is so much more satisfying in France. In the morning, we vote, and in the evening, we watch the votes being counted, knowing that ours is one of them even though we don't know which one it is. The results are gathered with the other voting places in town, and the tallies are posted at the city hall. They are then aggregated with results from other towns, and posted at the regional center. They are then further aggregated to sum to the national numbers. A beautiful hierarchical tree!

Fleas and Galton-Watson

Consider an ennemy Galton-Watson process where each node has 20 offsprings on average. If you kill 90% of the nodes, is that a success? No really: the remaining nodes are still a rather impressive number. How to destroy them, then? The solution is to repeat the destructive process a second time. If the second attack kills 90% of the remaining nodes, then you will be left with just a few sparse isolated surviving individuals who can then be killed one by one as they come out of their hiding places.

Apply this to flea infestation: I am lauching my second chemical weapons attack today, with stronger chemicals that leave a residue on floor and furniture, so that any egg that might still hatch in the near future would then be killed as soon as it is born.

Flea war

I have launched a massive chemical weapon attack in my house, ongoing as I write.

Fleas are a good example of an exponential process. One day, you think you might have gotten a bite but are not sure. The next day, you spot a flea. The next day, 5, the next day, your son complains that he can't work on the computer because fleas keep jumping on his ankles. Time to declare war! And that's why my house is currently being filled with toxic gas.

Where do those fleas come from? From a litter of kittens who were in my house for a few weeks. I knew they had fleas, but the fleas politely stayed on them and did not bother anyone else. I half-heartedly tried to bathe them and comb them with a flea comb, but my efforts were ineffective, and because of the youth of the kittens, there was no other possibility. After the kittens were gone, the flea eggs were left behind, and must have hatched in the last few days.

Infinity

Toothpaste I always thought of as an image of infinity: no matter how long you've been using a toothpaste tube, there is always a little bit more that can be squeezed out if you try hard enough. There is definitely a first time, but then you can always use it one more time. You never get to the end.

But last week I reached the end of my tube. It made a sucking noise, a hole appeared in the toothpaste, and, squinting through it, I could see the empty inside of the tube. First time in my entire life. Somehow, it makes me think of death.

Sour patch candies

One sour patch candy loose at the bottom of a backpack +
tablet +
chord +
a few days =
a big sticky mess.

Grading efficiently

Here is how I grade Theory homeworks.
1. Grade everybody's answer to problem 1, then everybody's answer to problem 2, etc. This goes much faster than grading all problems of the first homework, then all problems of the second homework, etc.
2. Read a couple of solutions by students who I know will probably get it mostly right.
3. After that, sketch a model solution; figure out the key points/keywords.
4. When reading a proof, scan it briefly to find the keywords. Ideally, someone using the right keywords has to have done the proof right, and someone missing a keyword has to be missing something in their argument.
5. Grade at a high level. Too much granularity means wasting time on unimportant details; some experiments have also shown, I have heard, that grades of the same exams by independent graders yield (paradoxically) more consistent results if the grading is more global. This means that I have to have a clear sense of "what really matters".
6. Occasionally give up. I typical spend the majority of my time on a tiny fraction of the homeworks (the ones that come up with a completely different approach, or from students who are unusually wordy and obscure, or a combination). Sometimes, if after some amount of time I still cannot figure out what their solution is about, I just add a note in the margin: "No credit -- I can't understand this. Come see me at office hours and if you can explain it to me you may get some credit."
7. Design homeworks so that they are easy to grade by the above method. In particular each question should have a reason for being there: it should test something specific, and then when I grade I am just looking for that key point. Example: ask for a proof by induction, in an application where there is a risk that the student may list the base cases wrong. When grading, I can then scan the whole proof and just zoom on the base cases. The rest is "noise" and I will essentially ignore it, although the student does not know it when he writes his solution. Some students then get annoyed because they will receive almost no credit even though, in their view, they got most of the question right; but they didn't figure out the one part I cared about...

Kittens and fleas

I am acquiring valuable knowledge on cat fleas. This time I have figured out that the kittens I'm fostering have fleas, before I got bitten even once.

1. They groom themselves more often than I am comfortable with

2. I closely examine the fur of the whitest kitten and spot some suspicious specks of black dirt

3. I pluck one speck, put it on a piece of white paper, wet it with water, wait a few moments: it dissolves and becomes reddish. That's the proof! It's not dirt, but flea excrement, made from kitten blood. How strangely gratifying it is to witness the definitive confirmation of one's fears.

Now that I have a head start on identifying the problem, I should be able to control it before we get infested. I hope.

Heartbreaking

The other night in downtown Providence, on Kennedy Plaza, I saw an older homeless couple. The man was carrying several heavy bags, and the woman was pulling a carriage. They crossed the street slowly, with slightly shuffling steps. On the other side, as the woman was having trouble pulling her carriage up, the man turned to her, saw what was delaying her, gently took the handle from her and pulled the carriage up the curb. They then resumed their share of the load and their slow walk.

A few minutes later, I saw them again, wandering back by the park, indistinct in the shadows but recognizable by their uncertain gait, before they finally disappeared out of sight.

More on technology

One more thing to worry about: I must not accidentally misplace my tablet pen - else lecture preparation becomes a real challenge!

A small miracle happened today: setting up my (borrowed) tablet in an unknown classroom with unfamiliar technological equipment, I followed the directions printed by the projector etc., pushed the buttons that had a big highlighted label, according to directions, and everything worked without a hitch. Amazing.

The alternative would have been a black board, and I hate chalk dust, so I was highly motivated to do it right.