Tuesday, September 23, 2014

Watch Your Back, Git

Changeset evolution is a big deal.  But nobody seems to be talking about it.  Well, except for this guy:

But even he says it's a small set of incremental improvements.  This is not small.  But it is all a little abstract right now.  Let's write a use case.

Friday, September 19, 2014

The Pendulum and the Winch

I often find that explaining computer science to non-computer-scientists is difficult.  It's been said that computer science is like no other field of study.  Well, I think that's a rather strong claim to make.  What follows is a translation of a standard problem in computer science into physics.  It is an analogy, unrealistic but nevertheless interesting.

I have a pendulum, supported by some apparatus ultimately connected to a pillar or pole.  It is possible to move the apparatus up or down, but only by manually detaching and reattaching it by hand.  I have a winch affixed to this apparatus which may raise or lower the pendulum.  It is connected to a coil of rope or string (which, for the purposes of this problem, is infinitely long yet magically takes up a finite volume), and can be remotely controlled at the press of a button.  The winch is also geared discretely; it only turns in units, and then only one at a time.

I wish to carry out a series of experiments involving varying the length of my pendulum.  In particular, I often want to lengthen the pendulum.  Most of the time, this setup suits me quite well.  But sometimes, I find I need a pendulum longer than the apparatus is high off the ground.  In these situations, I need to climb the pillar and move the winch up.  In so doing, I may need to start an entire experiment over again because the pendulum lost energy while I was climbing.  How can I avoid or minimize those climbs in proportion to the maximum length of the pendulum?  We must assume I do not know the maximum length in advance, perhaps because my experiments are highly complex and difficult to predict, or perhaps because they are directed by someone else's instructions, and they did not think to tell me in advance how long a pendulum I would need.