Friday, December 31, 2004

e is for error correcting

random thoughts on new year’s eve. error correcting codes are cool.


I haven’t fully techie dorked out in a while (too much of a social scientist, sigh), so I thought I would explore this random part of my mathematics/computer science curriculum that comes up in weird random places: error correcting codes.

the basic idea is that an amazing number of parts of human life can be thought of as encoded message transmission: dna, language, music, art, puzzles. At mit, a large number of classes dealt with encoded message transmission but only recently have I started appreciating the broader applications.

a recent American scientist article talked about the efficiency of the dna-codon to amino acid coding. everyone knows that there 64 (corrected) possible codons (length 3, with 4 base pairs) but only 20 something amino acids. What’s cool is how amazingly efficient the encoding is, that allows functionality up to random errors in the signal.

This is the same idea behind how cell phones work to carry voice messages, how cd’s work to store music, how mp3s compress music, and many more. this train of thought was largely inspired by the adverts for dialup modem speed enhancers, which reminded me of the power of z-modem over Kermit and x-modem.

a code can be thought of as a subset of a message space. efficiently designed error correcting codes have an associated distance metric that places different code words as far apart as possible, so that many errors in transmission are necessary before you mistake one code word for another. the English language is such a code. i cna tpye a vrye grrbllde emssgge adn yru cyn ltlll rped it. economist ariel Rubenstein and others discuss the optimal design of languages.

a fun simple experiment is to run pkzip on a text file, and you’ll be able to demonstrate to yourself that English and in fact most languages has a message space 8 times larger than the code space. each letter in a paragraph typically conveys only about 1 bit of information.

other fun applications:

economist glen loury believes that the identities we use are codes to truthfully transmit information about ourselves, and then argues that the codes African Americans use are inefficient and self-defeating.

in analog signal processing, the nyquist frequency is a nice analog to what’s going on in this digial coding/encoding.

my favorite application is a riddle that I will end with. 10 prisoner’s are told they are to be executed. they will be lined up single file and each will be given a hat, black or red. They will be lined up in such a way that each prisoner can see the hats of each person in front of him, but not his own. The person in the back can see 9 hats, the person in front of him 8, the person in front can see none. From back to front, each prisoner will be asked to say either black or red. If he says the color of his own hat, he is saved, if not, he will be killed. Find the algorithm that in expectation, saves the most number of prisoners.

(Hint: 9.5 prisoner’s can be saved…)

Friday, December 24, 2004

d is for doping

Random weird connection. Some talk show on NPR talking about the recent sports doping scandals made the interesting connection between sports doping and other realms of performance enhancing drugs, i.e. academics and music. I never personally knew of anyone who was into sports enough to be a likely steroid user, so the prevalence of it though widespread didn’t really hit me.

But the expert suggested that there are college students who take un-prescribed Ritalin to help them study for exams, and musicians who take beta blockers to help them escape stage fright. I know people who do both.

Who knew that Ritalin, miracle treatment for ADD would work for anybody to provide added focus. And then you have to wonder, is it really wrong.

It was shocking how casually this one girl admitted to the Beta Blocker trick, for a high school violin recital of all things. These drugs prevent your heart rate from increasing. It is something I can relate to very well. I pretty much choke every audition I’ve ever been in, because my heart must triple in speed to a rate I never feel in any other situation, including exercise. But a drug seems like a ridiculous measure. The girl joking warned to be careful. She had gone jogging after the recital and passed out because her heart couldn’t provide enough oxygen since it couldn’t beat fast enough.

Monday, December 20, 2004

b is for bookstore

for a time, I never understood bookstores (at the time, these to me were lifeless interchangeable national chains) when one could have an infinitely wider selection online at amazon, until I realized that today, a bookstore is not valuable for how many books it carries, but how few. (see also my epinions note: http://www.epinions.com/content_1459593348 )

editors are important to tell us what's important. Which is why record companies and tv networks will always have a job, even when content becomes essentially free. we need people to tell us what’s good.

when it comes to bookstores, a good one will tell you which few amongst the universe of millions are worth reading. and your favorite, will be the one that fits you, speaks to you. two have succeeded for me

thus, the best bookstores at doing that for me, is firstly the MIT press bookstore, a tiny bookstore across the street from the main campus bookstore, stocked to the brim with fascinating books related to all the knowledge MIT is interested in, from nanotech, to social networks, to typography, to urban design to poetry. the place is crammed with books that pique my geeky fancy.

recently, I rediscovered Kramer books in Dupont Circle in Washington DC. Aside from having a nice bar, live music and great desserts, this store reflects the social scientist in me. every book on display in there from hip snooty fiction like Chabon and Umberto Eco to pop intellectuals like Krugman, to general interest social science on topics like cultural social psychology, I’ve either read, want very much to read, and all I could bull shit about at length.

today I add a third for different reasons. Dewey’s Comics in Madison, NJ. A store I frequented a bit in high school about a decade ago, and liked especially because of how incredibly nice the owner was/is. in stark stark contrast to the jerk who owned the other local competitor Fat Moose. I tried to go back and now and then on visits home, and happening to be in Madison today, I stopped in. It’s been four years since my last visit (I know because I first went to their old location, which apparently they left 3.5 years ago). The owner was still there, and he still remembers me, though it’s been 9 years since I’ve been a regular customer. He even recalled seeing me in USA today. It felt like home.

Friday, December 10, 2004

divertissements - diversions

I have a lot of hobbies I noticed. At most of them, I am either the worst of those who are good, or the best of those who suck. Like I play clarinet for various Stanford musical theater productions. I'm typically the worst musician there, but passable at least. I still play a couple times a year, so I'm better than the great majority of those who played in high school and then gave it up.

At hockey, a bunch of us absolute beginners started playing a couple years ago. After a bunch of ringers started playing, I'm one of the only one of the original gang that still comes. So I'm better than all those beginners, but the worst one there now.

At chess, I'm good enough to know how bad I am, which is quite a feat. I know what a queen's gambit acepted is, and the importance of initiative, but that doesn't stop me from losing the initiative to Adam every time we play, and for him to whoop my butt every time.

Anyway, I only bring these up because last week, for these things. My mind was largely occupied with my own research (I gave a seminar at the end of it), and so I got crushed at chess, and poker, and had a shitty performance.

But this week, seminar over, brain unoccupied, I kicked ass at poker (won $45), did well against adam at chess (won like 2 out of 6 games, twice as many as I've ever won against him before), and had a kickass performance as the clarinetist for Gilbert and Sullivan's HMS pinafore.
ok, enough babbling.

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