Programming

Shuffling a collection of items is a surprisingly frequent task in programming: essentially, it comes up whenever a known input must be processed in random order. What is more, there is a delightful, three-line algorithm to accomplish this task correctly, in-place, and in optimal time. Unfortunately, this simple three-line solution seems to be insufficiently known, leading to various, less-than-optimal ad-hoc alternatives being used in practice — but that is entirely unnecessary!

The Nelder-Mead-Algorithm (also known as the “Simplex Algorithm” or even as the “Amoeba Algorithm”) is an algorithm for the minimization of non-linear functions in several variables. In contrast to other non-linear minimization methods, it does not require gradient information. This makes it less efficient, but also less prone to divergence problems. In contrast to other methods, it is not necessary for the minimum to be bracketed by the initial guess: the algorithm performs a limited “global” search. (It may still converge to a local, rather than the global extremum, of course.) Finally, the algorithm is fairly simple to implement as a stand-alone routine, which makes it a natural choice for multi-dimensional minimization if function evaluations are not prohibitively expensive.

When writing programs that do computations, my overwhelming preference is to simply write results to standard output, and to use shell redirection to capture the output in a file. In this way, I am leveraging the shell’s full functionality, in particular filename completion, in the most convenient way possible. For the file format itself, I prefer simple, column-oriented, delimiter-separated flat files. They are completely portable, and can be read and understood by most tools. (They also play well with the usual Unix toolset.)

But this simple approach breaks down, once a program has to write more than one output stream: for example in the case of a simulation run, I may want to capture periodic snapshots of the simulation itself, but also track various calculated metrics as well. These two streams will not fit comfortable into a single flat file. One option is to use a structured file format, the other option is to write to multiple files simultaneously.

Among my favorite features of the Go language is the fact that Go has concurrency and network programming “natively” built in. It reflects Go as being designed for the 21st century, where the network is as much taken for granted as the filesystem was towards the end of the 20th.

As cut-n-paste examples, here are skeleton implementation of both an HTTP server and an HTTP client. These implementations are intentionally bare-bones, so as not to obscure the most relevant points. It should be easy enough to extend them as desired.

Imagine a shared resource, such as a compute server. Users can submit jobs to the server. The resource is “free”, in the sense that no costs are imposed on the users. The question is how to best assign and prioritize jobs when multiple users submit jobs simultaneously.

Over the holidays, I sat down and wrote a casual turn-based strategy game. Aside from the obvious fun aspect, one major motivation was to gain experience with the pyglet game library, which I wanted to evaluate as a potentially general, light-weight GUI library for Python.

Over the holidays, I had the opportunity to work on a spare time project, and so I sat down and wrote a casual, turn-based strategy game; a variant (you might say: a clone) of the KDE game Konquest.

Finding a realistic (or at least, realistic looking) initial configuration of game objects or simulation particles can be a challenge. The desired configuration should appear to be both “random” and at the same time “spatially uniform”, without objects clustering together or overlapping.

I have started to get interested in Hidden Markov Models (HMM). As a warm-up, I prepared a pure Python implementation of the relevant algorithms (github).

In a moment of nostalgia, I picked up my copy of “The Art of UNIX Programming” by Eric S. Raymond (esr) and flipped through it again. It’s a book I’ve had since when it came out in 2004, and that I’ve always been quite fond of. I was looking forward to a review of “the way the future was”, as viewed from the early 2000s. So, it came as a bit of a surprise to me to find that the book seems to have aged rather poorly.