Rosio Pavoris a blog

A decent proportion of my readers are noobie programmers or people who aren’t in a position to receive a formal CS education, so I thought I’d cover the basics of a fundamental concept most people cover in their first semester of algorithms or AI today: search trees. The fact that my college considers this to be third-year material so advanced they cannot in good faith make the class compulsory is neither here nor there.

Consider the famous problem of the farmer who wants to cross a river with his fox, goose, and grain, though the only boat can only carry himself and one of these three possesions. Ignore for a moment why a farmer would own a fox, and let’s stretch credibility a bit more by assuming that while the fox and goose are well-trained enough not to wander off in the absence of the farmer, they are not trained not to eat the goose or the grain, respectively, in said absence. How can he safely get to the other side without losing his goose or grain?

Read the rest of this entry »

Having finished another popsci book on chaos theory recently (Ian Stewart’s Does God Play Dice?), I thought it’d be an interesting exercise to visualise the Lorenz attractor, and since it’s been a while since I’ve done anything new in programming, to take the opportunity to get into Xlib, the X Window System C library. Results aren’t very encouraging.

I mean, I got something to work easily enough, but any attempt at introducing color beyond black and white for clarity fails miserably and in non-deterministic ways. Eventually I gave up and redid it using something I know.
Compare:

(It’s prettier animated, so do compile the code yourself and see.)
In both cases, the screen represents the Cartesian plane (X-axis horizontal, Y-axis vertical, origin right in the center; one unit is ten pixels). In the Xlib version (left) the Z component is ignored entirely (so it’s really a projection of the attractor onto the Cartesian plane), in the Allegro version (right) some attempt at representing it using shades of gray has been made, with z=0 being black and z=55 being white (though because it is drawn with no real care, it will happily scribble dark lines over light ones if it has to).
You can mess with the variables and starting condition to see how it behaves, or swap around some Xs and Ys and Zs to get different angles, and at least in the Allegro version, messing with color is trivial enough.

Which brings me to my question: does anyone know of decent introductions to Xlib? The Internet is full of tutorials, and as usual, all of them seem to suck. I know Xlib isn’t really supposed to be used directly, but I want to.