Martin Geisler Online

The weather is finally getting better: the sun is shining and the temperature has reached 15 °C several times. It’s wonderful to be able to be outside without having to wear thick gloves all the time. It’s also as if my daily ride to and from Aarhus University is shorter know that the weather is improving…

Tomorrow is a Danish Holiday so this weekend will be a little longer than normal. I should probably use some of that time to read in my books: the time for my exams are moving closer. I have four exams this semester: written and oral exam in Mat11 which is Mathematical Analysis, written exam in SS1 which is Statistics and Probability Theory 1, and then another written exam in dADS which is Algorithms and Data structures in Computer Science. I only had two exams last semester, so this is a little frightening.

Well, I’ve done various stuff — Jérémy and I have made the first third of the mandatory assignment in dADS. It’s actually an interesting assignment: we have to design an algorithm that will find the maximum matching in a bipartite graph. The first thing we had to do, was to prove that an algorithm written in pseudo code was valid and correct. The algorithm uses a transition system to color the nodes in the graph, so we had to prove a couple of things about that too.

This week we have to design efficient datastructures that will allow us to color the graph using the transition system in time O(m+n) where m is the number of edges in the graph and n in the total number of vertexes. We will use these datastructures in the final third of the assignment where we have to implement the algorithm in Java. Exciting stuff…

I plan to publish the report here at gimpster.com when we’re finished, so stay tuned. (It’s in Danish, so don’t be too excited if you cannot read that :-)

It’s been a while since my last post — I’ve been busy. One of the things I’ve been working on is [PHP Weather][]. And the cool thing is that I’m not alone: Max Hammond has helped me a lot. He has made the beautiful logos you see here and on http://phpweather.net — he also bought the new short address.

One of the cool new things is the updated Configuration Builder which helps you build a correct configuration file.

The framework is actually usable for other projects as well if it is adapted a bit. It works by presenting some options to the user. The input is checked at the client using JavaScript and at the server by PHP. Depending on the input more options might appear — this is controlled by the options dependencies on other options. The idea is, that the user wont be asked to fill in a database-password unless he has selected a database-type that requires a password.

So, things are moving in the right direction — you should come and join us if you want to help. There’s plenty to do: if you cannot code, then perhaps you’ll be able to go through the comments in the code and correct some of the more embarrassing spelling errors I’ve made :-)

Manitou and I met yesterday and made a couple of Java assignments which were overdue. We implemented a Heap using the Locator pattern and a Vocabulary using a Trie — it was a very good learning-experience to actually implement these ADTs instead of just talking about them.

We also talked about other things — we met at 14:00 and went home again at 23:30 so there was plenty of time :-) One of the things we discussed extensively was, that he had a book, which said, that the set of all subsets of the empty set, which is denoted 2^∅, is {∅, {∅}}. I don’t believe that this is true — the only subset of ∅ is ∅ itself, so I would say that 2^∅ = {∅}. If 2^∅ = {∅, {∅}}, then that would imply, that ∅ ∈ ∅ which is clearly false, as the empty set is empty. We’ll ask Jørgen Hoffman-Jørgensen about it — he should know as he’s our teacher in Probablility Theory.