The earliest memory I have of ‘programming’ is in the early/mid 90s when my father brought home a computer from work. We could play games on it … so of course I took the spreadsheet program he used (LOTUS 123, did I date myself with that?) and tried to modify it to print out a helpful message for him. It … halfway worked? At least I could undo it so he could get back to work…

After that, I picked up programming for real in QBASIC (I still have a few of those programs lying around), got my own (junky) Linux desktop from my cousin, tried to learn VBasic (without a Windows machine), and eventually made it to high school… In college, I studied computer science and mathematics, mostly programming in Java/.NET, although with a bit of everything in the mix. A few of my oldest programming posts on this blog are from that time.

After that, on to grad school! Originally, I was going to study computational linguistics, but that fell through. Then programming languages (the school’s specialty). And finally I ended up studying censorship and computer security. That’s about where I am today!

But really, I still have a habit of doing a little bit of everything. Whatever seems interesting at the time!

Bitvectors in Racket

2012-10-29

A bit shorter on time today, so I’ve just got a quick library that I worked out to solve another problem (I’ll post it later this week when it’s actually working). Basically, when you need to store a heck of a lot of binary flags and don’t want to waste space, the best way to do it would be as one long list of bits. It’s really easy to do in a language like C, but how can you do it in Racket?

Pythagorean Triples

2012-10-27

When Programming Praxis mentioned that the newest challenge sounded like a Project Euler problem, they were’t wrong. Basically, the idea is to count the number of Pythagorean Triples with perimeters (sum of the three numbers) under a given value. The necessary code to brute force the problem is really straight forward, but then they asked for the count up to one million. With the brute force O(n^2) algorithm (and a relatively high constant), that’s not really feasible. So that’s when we have to get a bit more creative.

Determining country by latitude/longitude

2012-10-25

Yesterday I talked about how I used censorship research) where the API will report longitude and latitude but not always country.

Determining country by IP

2012-10-24

In my line of research, it’s often useful to be able to identify where a country is using just it’s IP address. I’ve done it a few different ways over the years, but the simplest I’ve found is using the MaxMind GeoLite Country database directly. To speed such lookups, I’ve written a simple Python script that can run a whole series of such queries for you.

Prime Partitions II: The Listing

2012-10-22

As the continuation of Saturday’s post on counting the number of prime partitions of a number without actually determining what those partitions are, today we’re going to work out the actual list of partitions.

Prime Partitions

2012-10-20

Today we’re back into the mathy sort of problems from Programming Praxis, tasked with calculating the number of prime partitions for a given number–essentially, how many different lists of prime numbers are there that sum to the given number.

For example, working with 11, there are six prime partitions (I’ll show the code for this later):

> (prime-partitions 11)
'((2 2 2 2 3) (2 2 2 5) (2 2 7) (2 3 3 3) (3 3 5) (11))

Unfortunately, the number of prime partitions quickly gets ridiculous. Once you get to 1000, there are 48 quadrillion prime partitions… So generating all of them isn’t exactly feasible.

Memoization in Racket

2012-10-20

Memoization is awesome!

I’ve already written one post on the subject in Python, but this time we’ll do the same in Racket. It’s particularly timely as without it, today’s post on determining the number of prime partitions of a number would take longer to run than I care to wait.

Small projects source code on GitHub

2012-10-19

I’ve just gone back through all of my older posts in the Small Projects category and uploaded most of the source code to GitHub. This will let me maintain the code on a local git repository and should make updating projects easier, rather than having to update them on my web server.

Also, syntax highlighting! Everyone loves a good syntax highlighter.

In any case, you can access all of the code that I’ve posted thus far here: GitHub: jpverkamp

The Evolution Of Flibs

2012-10-18

In the past, I absolutely loved messing around with genetic algorithms. The idea of bringing the power of natural selection to bear to solve all manner of problems just appeals to me for some reason. So when I came across a puzzle on on Programming Praxis called flibs source code The eventual goal will be–given a binary sequence–to evolve a finite state machine that will recognize the sequence and output the same, offset by one.

Rule 30 RNG

2012-10-17

Today we get away from the word games for a little while and get back to talking about random number generators (previous posts here and here). Or rather one random number generator in specific: a Rule 30 psuedo-random number generator (PRNG). (Here’s the motivating post from Programming Praxis.)

Remember the previous post I made about cellular automaton? The basic idea is to turn those into a random number generator. If you go back to the linked post in particular and give it Rule 30 with a random initial state, you can see how chaotic the rows seem to be. Perfect for a PRNG.