On joining the ACM

I joined the Association for Computing Machinery (ACM). I admit, I went back and forth on it for quite some time. When I was an undergraduate taking my most influential and self-defining class, the professor urged us all to join IEEE (Institute of Electrical and Electronics Engineers). But when a student asked the professor about ACM, he scoffed: "Oh, ACM? I let that lapse when I was a sophomore in undergrad." So, of course, I went home that night and joined the IEEE as a student member. Years later, I was elected vice-chair and served as the interim chair of our branch. Unfortunately, but not surprisingly, given the amount of faculty support it received, the ACM student branch on our campus died out over a decade ago. The IEEE student branch is still active.

I joined the ACM a month ago or so because I was submitting a poster to an ACM-run student research competition. There was a requirement that, if the poster is accepted, you have to be an ACM member. But I decided I would join anyway. The student membership is relatively inexpensive, I thought, and I may as well try it out.

When I received my first Communications of the ACM (CACM) magazine, I was blown away. It was easily three times thicker than the meager IEEE Spectrum magazine. Whereas both live in my bathroom, I find the CACM has hours more reading material in it than the Spectrum. And it is interesting, and enjoyable.

Take, for example, student and faculty attitudes and beliefs about Computer Science. It is about how students' beliefs about computer science as a discipline and as a way of thinking converges with or diverges from faculty consensus. Where the students diverge from faculty, there is a (arguably) a curriculum gap that needs to be fixed.

Also, the ACM membership card is nicer, and the website is cleaner, faster, and much less buggy than the IEEE website. It is clear that the IEEE website was written by electronics engineers, not programmers!

Guard, sticky, and round

What follows is a sex joke about floating point numbers.

Irrational numbers are ones that may not terminate, or may repeat forever. For example, the number pi is irrational (because it neither terminates nor repeats), and so is the decimal representation of 5/9=0.555555... (because it repeats forever).

There is a problem. How do you represent an irrational number digitally? You have only a limited number of bits... and possibly an infinite number of digits to encode.

The IEEE-754 standard for floating point numbers defines rounding modes. These modes are used to try to shoehorn the (possibly infinitely long) number into a finite number of bits. The standard defines functionality with which you can round up, round down, truncate, and round to even.

What makes it happen are the guard, round, and sticky bits. The guard bit is the first bit that not fit into the representation. The round bit is the second bit that does not fit the representation. Finally, the sticky bit is a bitwise-OR of all the bits after the round bit.

OK, here's the joke. It's kind of a stretch, but stay with me...

Rounding is like sex.

You gotta use the guard bit.

If you don't, you get the sticky bit.

And then... well, you're round.

May 8: 65th Anniversary of Day of Victory, and the Siege of Leningrad

The siege of Leningrad, now and previously St. Petersburg, lasted 900 days and cost one million lives to starvation alone. But the numbers don't tell the whole story: they are just a statistic.

My grandmother survived the siege of Leningrad. She lived in the city and watched her dearest relatives die during the years between 1941 and 1944. She survived the siege with her mother, who, just four years later, died of cancer in 1948. She rarely talks about it, but three times a year she brings it up: the anniversary of the beginning of the blockade, the anniversary of the end of the blockade, and the anniversary of the day victory over the German forces.

Each year, I look it up on the Internet, and listen to what little she tells me about it. Each year, I have had the same emotional response: intense, deep sadness, and a hollow feeling in my core.

But now that I have had a child, it hits me so much harder. This is not something that happened to people in Soviet Russia 65 years ago. This is something that happened to me and my family. Weeping, I watched documentary YouTube videos explaining the siege, and showing families torn apart by starvation and bombings. Bodies of children, wrapped in blankets and carried by sleds to the river. One hundred twenty-five grams of bread, half of which is made of sawdust, doled out as a daily ration. And in the videos, the streets are packed with people going somewhere. Where are they going? They go in all directions, but where? Everything is frozen; everything is dying.

My grandmother told me about the grass that grows in the spring. She said it was the most magical thing: after months and months of no food, no rations, and death (in the worst of it, 700 to 10,000 people died every day), the first sprigs of grass that sprung up were celebrated as a sign of hope and life. People would gather and look at the sprigs, and eat them for vitamins and freshness.

How can anyone survive the siege with her body, but having lived through it, survive the siege with her soul?