Playing around with Embedded Objects in IE

Yesterday I felt like playing around a bit with embedded objects in IE - you know, showing Windows Forms in a browser. An old .NET trick that I've used a couple of times.

For some reason it has never quite become the market standard it was supposed to (probably because it's ugly, inefficient and very browser specific) - but it would have been nice with a good alternative to java applets!

I made a quick adaptation of the SudokuSolver from my previus post to see how it would work as an embedded object. This is what I did:

1. Made a Windows Forms Library project
2. Made a Windows Forms User Control
3. Moved the UI from the Sudoku application to the new User Control (as well as the Code Behind)
4. Compiled and put on a web-server
5. Made a HTML Page that includes it as an embedded object, and put the page on the same webserver (this is important)

This is the HTML I used, notice how you provide it with the URL to the Windows Forms DLL, and then the full path (including namespace) to the control to display:

    <object id="SudokuControl" height="240" width="206"
        classid="http://www.thraen.dk/Download/SudokuWinLib.dll#SudokuWinLib.Sudoku">
    </object>

If you are watching this blog in IE, and you have .NET 2.0 installed, and your security settings is just right, there is a chance that you might actually see the Sudoku Solver here:

Solving Sudokus as CSP with Forward Checking

When you think about it, a Sudoku is a perfect example of a Constraint Satisfaction Problem, and so it made good sense that the final programming assignment in the IAIP course I'm taking was to solve a Sudoku as a CSP, using forward checking.

The basic idea is to define the problem as a set of variables (in this case 9*9=81 variables), where each has a finite domain of potential values (by default values 1-9 in this Sudoku example) and then there's a number of constraints connecting the variables. For the Sudoku these constraints ensure that the numbers 1-9 are distinct in every horizontal and vertical line, as well as in the same 3x3 square.

Once the problem is defined as a CSP there's several approaches to solving it. The assignment this time was to implement Forward Checking. The basic idea with forward checking is to make a backtracking depth-first search in the solution space, but every time a variable is assigned, the domains of all the affected variables (due to constraints) will be modified. If a domain becomes totally empty, we backtrack. It all sounds terribly complicated but it's really a straightforward approach, assigning the variables one at a time and whenever something is assigned revise the possible values for the rest of the affected variables.

As usual we were supplied with a nice codebase to extend to (in fact all we had to do was more or less to implement the Forward Checking part), but also as usual the entire codebase was in Java. This time it made the most sense to simply port it to C# and it didn't take much more than an hour to port the main solver class and even refactor a little.

The report can be seen here.
The project files can be found here.

Solving NQueens using Reduced Ordered Binary Decisision Diagrams

Here's one of the things I've been too busy to post:
At my AI course we've completed our last 2 assignments. The one that I'll post here is the N-Queens problem solver, that helps solving the n-queens problem using BDD's.
BDD's is a really clever technique that can help solve some satisfiability problems quite fast.

The N-Queens problem is a classic problem, described lots of places. The derives from the 8-queens problem, thats how to fit 8-queens onto an 8x8 chess board without any of them threatening the others (according to the rules of chess).
It can be solved in many ways, but BDD's is a quite efficient way of doing it.
The basic idea is to build a binary decision diagram, where every node corresponds to a variable in the problem, construct the diagram according to the rules (constraints) that apply to the specific problem and along the way reduce the diagram according to a couple of rules (and to avoid duplicate node-childnode patterns).
How we choose to assign the nodes can be found in our report (as always written with Thomas Gravgaard and Peter Thygesen). Also, a final web-version of our solution can be tried out here.

The joy of being unemployed!

Ahh..posting again... I know, it's been a while, but now I hope to be back again. Now I've been through the first month of unemployed life, and I must admit that it has been nothing like I had imagined. It's been crazy! No time for sitting in front of the local supermarket drinking 6-packs of beers all day (as I had been told unemployed people are supposed to do), no time for playing around with technologies and ideas (as I had hoped) and no time for blogging either...Well, perhaps it's just a bad excuse, but I've been really, really busy.
During the first couple of weeks I got contacted by 40+ companies that wanted to discuss job oppertunities! Early on I was really eager and polite and noted everybody down and did my best to keep track of them, but I must admit that after a couple of weeks I started to sort them roughly at the initial contact. For instance I turned down all consultancy companies, cause I don't feel like body-shopping. At least not now.
But even with thoroughly sorting it mounted to around 15 initial interviews I had to go to. This part is really terrific and quite an ego boost (currently my bloated ego has reached a size where it can hardly fit into living room), that can definetly be recommended. Each interview was around 1,5h - most of the time talking about one of my favourite subject, me. As you can imagine it took quite a lot of time to go through all these talks, and following up on them afterwards. Meanwhile I constantly kept track of all advantages and disadvantages to each job, and after a couple of weeks of initial interviews I had a list of 10 companies offering me 15 different jobs, ranging from software architect, product manager, senior developer to researcher.
Then it started getting tricky!
Cause all these jobs on my shortlist sounded really good and I could easily see myself enjoying each and every one of them. But only one can be picked. So I decided to measure companies on more criterias and narrowed down the list to 5 companies that I decided to have a second talk with.
Now I'm down to considering 3 companies, and of those I must admit I do have a favourite - but I'm not telling which - at least not until the contract is signed and everybody's happy!