Progress report for week 39

Good news, bad news. The bad news is that my laptop still hasn’t been fixed and I’ve had some trouble accessing the BOINC homepage lately, so I haven’t got a chance to download and test it for myself. I keep getting “connection timed out” when I’ve tried accessing it from school and at home.

The good news is that I’ve received two much needed reference books:

  • “The C Programming Language, Second Edition” by Kernighan and Ritchie
  • “The C++ Programming Language, Special Edition” by Stroustrup

I admit that I liked Kernighan and Richie’s book best because it’s about 700 pages shorter than the one by Stroustrup and it’s more to the point. I’m thinking about reading the C book from beginning to end because I like K&R’s writing style. Even though C++ is a more comprehensive language than C, a significant portion of the content in the C++ book feels superficial. It’s a good reference book, but not one that I would read from beginning to end. In that respect I prefer Bruce Eckel’s two “Thinking in C++” books.

I finally wrote the missing code for initializing the “boolean matrix circular quad-linked list” (BMCQL) data structure used by the DLX algorithm. That means that the libdlx library is more or less functional. However, not everything went according to plan. I spent about 6 hours to debug some silly mistakes I did in a couple of getters and setters. I was almost certain that I was doing something wrong with some of the pointers, but strangely enough they appeared to work without a hitch. On the bright side at least I gained a much better understanding of how pointers work.

A program using libdlx to solve exact cover problems has also been written. I’ve simply called it “dance”. It has been used to verify that the DLX algorithm has been implemented correctly. I’ve only tried it on a couple of small matrices I have written by hand, but I’ll soon test it on some n-queens problems as well.

By successfully implementing the DLX algorithm the first milestone of the project has been achieved. The completion of the second milestone will be announced as soon as I’ve been able to verify the correctness of the implementation by running it through some of the n-queens problems.

I’ve added some pseudo code to the report about the BMCQL data structure initialization and written more about the implementation. The dance program and the DLX library version 0.1 has been released on Google Code. The binaries are only available for Windows, but it shouldn’t be too much of a problem to compile it in Linux. A basic makefile will be added shortly.

Update: As you might notice I also figured out how to reorder the posts into reverse chronological order. Unfortunately I’ve been unable to find my way back to where this functionality is hiding so this post is stuck in the wrong position (at the bottom).

Update: After some research I found the ordering functionality. On the Portfolio page where you have a list of the portfolio elements you have to change the category. Use the drop down list on the right side and change it to “No category” (or whatever category you’re trying to sort) instead of “All” in order to access the ordering mechanism. Makes perfect sense, right?

Update: The BOINC homepage appears to be back online.

NOTE: This post has been imported from my old it’s learning ePortfolio DECS blog.


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