Sunday, April 09, 2006

Subsumption Rules.


Arrived in Lisbon at about 6 p.m.-ish after several delays, including the baggage claim, which took forever because bike is "special oversized" luggage and it seems sometimes like no one has ever seen one before. Anyway, it arrived a bit more beat up and broken than I was expecting (it seems to have taken several sideways falls), so spent a full hour in the airport fixing it and re-arranging the contents of the panniers, which had been opened at SFO airport for security checks. When I opened my panniers to see the toolbag missing, I panicked, for without it, I couldn't put the bike back together (for flying you need to twist the handlebars and remove the pedals). Luckily, however, they did not confiscate it, as it turns out they simply had painstakingly taken out every single item from the panniers and scrutinized it carefully, including unfolding of T-shirts, before putting them all back together fairly helter-skelter. Still, you have to hand it to them, when they show some consideration by at least attempting to fold back your clothes. So my irritation passed quickly upon observing this.

Getting the bike from the airport into town was a bit troublesome. The info desk claimed you can take it on the bus, but, as it turns out, that wasn't true according to the bus driver. Then, I attempted to load the bike (wheels removed) onto the back of a Mercedes Benz taxi, but the driver was not helpful and was quite adamant in not taking me with the bike. Eventually, a kind policeman flagged down another taxi, who had a better sense of humor than the first one. All in all, up until arriving at the Youth Hostel, a rather stressful time. (Consider, too, that I hadn't slept much in the past two days, since immediately after selling my car on Thursday afternoon the rest of the time was spent packing and running errands nonstop, including well into the night/early morning hours, and if it hadn't been for a set of close most kindhearted friends who pitched in with the packing and moving help at the last minute--on the very day of departure, no less--there's no way I would've been able to make it.)

Anyway, arrived here no problem, Youth Hostel (Pousada de Juventude de Lisboa, Rua Andrade Corvo, 46, 1050-009 Lisboa Tel:(21) 353 26 96) had place enough for me, and it is a very clean and comfy place, quite centrally located. At last, I could breathe freely, all responsibilities and worries left behind in a closed set of boxes and a storage space, the world left to me for the taking.

Now what?

Perfect freedom is such a useless concept. Every optimization problem requires some constraints, and any optimal decision making involves evaluating costs and benefits which, in a perfectly free system, are nonexistent. Even behavior requires some sort of systematic regulation (a moral code for instance, or etiquette rules, social conventions, personality, or biology, even), whether consciously or unconsciously chosen in view of one's own past experiences and observation of others' experience, or uncontrolledly inherited or involuntarily imposed, even, by one's upbringing and cultural background.

But when one is an uprooted stranger travelling in a foreign country, one can even attempt, if desired, to try to modify said constraints, because, being an unknown person in a new environment, there is no prior history of behavior in the new place that needs to be kept consisistent with the current one, and, since the stay is also temporary, the consequences of behavior are also a bit more relaxed, because you don't really have to live with them as much as if you had to stay. In my particular situation of the moment, too, there are no manner of economic concerns, or sentimental attachments to places and things, nor responsibilities to other people. A fine place to find oneself indeed, at least once in a lifetime. And while most people try in their teens to bend their rules as much as possible while freedom such as I just described is typically not granted to them, and the inherited rules of behavior have not been yet sufficiently put to the test by life's experiences, in my situation, by now, the deeply rooted "rules of thumb", including issues of morality, personality, and value systems have already been rather well tested and set.

This is not to say, of course, that I cannot nevertheless enjoy a kind of fun and liberty that most people never have available. However, this does not obviate the need for the creation of a few guiding principles to accomodate my particular, a lot more free of responsibilities and worries, current situation.

Back at MIT's AI Lab, Prof. Rodney Brooks came up with a system to make robots behave, or rather, appear to behave, intelligently, based on a simple hierarchy of rules. Basically, complex robot behavior is described, instead of on a case by case basis (if situation A, do X, if situation B, do Y instead, etc) like most traditional algorithms, by a set of simple instructions with a well-defined precedence rank. Basically, the robot just putters around running the lowest-level rule programmed into it, until the situation arises when another rule takes precedence over the lowest level rule. For instance, suppose we want to make a robot modelling a human-fearing but light-seeking insect. We might then create the following three hierarchy rules:

1. Wander about the room aimlessly
2. Seek the light
3. Run away from humans.

In this scenario, the rule with the highest number takes precedence over the lower-numbered rule. So the robot wanders about the room aimlessly until one of two situations occurs: a) a human approaches, or b) there is light in the room. Depending on situations a or b, the robot behaves accordingly, running away in one case, and approaching the light source in the other. And in more "complex" situations, say, when a human is carrying a light, the robot simply behaves according to the rule that has precedence, in this case, by running away, since that rule is higher on the scale than the "seek the light" one.

For this simple example, this system is hardly any different from a bunch of "if A, then do X, if B, then do Y, if A and B, do Y", but if you consider that a robot may have 20 or 100 different sensors and "stimuli", if you will, it must react to, then considering all possible combinations of A, B, and C ad infinitum stimuli becomes a very, very cumbersome task for the programmer (whom at this point, if he still insists on programming in such a manner, I am now allowed to call naive). Brook's system, is, of course, then, a whole lot simpler, because given combinations of stimuli, even combinations one has never thought of, all the robot has to do is apply the rule that has the highest precedence rank. He called this system "subsumption architecture", because the highest-precedence rule then hides, or subsumes, all the rules that are positioned lower in the hierarchy.

So, back to where we were. I think that for my current situation, my behavior needs some subsumption architecture modelling. After some thought, I came up with the following 3 simple subsumption rules, ranked top to bottom (i.e. highest priority rule at top of list):

1. Be safe.
2. Befriend the locals.
3. You are in no hurry.

Cool, huh? Very simple, but so elegant! The "befriend the locals" rule takes care of making sure I try all the local cuisine, experiment butchering the local language in conversations with the residents, attend music and folk dance and art performances, get lost in city centers, and all that good stuff. Rule number 3 ensures I have plenty of time to do this as well as time to rest, and is the default operating mode, because unlike most vacationers who need to get back at some point to their boring and stressfull jobs, I wake up every day from now on happy and excited and looking forward to a new day full of adventures, and that's a good thing.



Anonymous said...

Grandioso! Specialmente il discorso sulla libertà e su questa ultima scala di priorità: mi tranquillizza un po'. Ciao.

Anonymous said...

You Go Girl!!!
Have fun. :)

Walid said...

Wow, Elisa. I'm bowled over.