I got a big interview tomorrow. A massively big interview. The one I’ve been preparing for all along. It’ll be all day long from 7:15am to 6:00 pm, but its worth it, because this is a DREAM job! Its with Direct Energy for their Direct Energy IS Leadership Developement Program. I’m undoubtedly nervous, and a bit scared. Whenever I’m scared, I like to sing about my favourite things:

Coding in linux and fixing my software,
Running Ubuntu and trees that will compare,
Studying physics and theories with strings,
These are a few of my favorite things!

Solving equations and eating cheese noodles,
Searching and working and chatting through google,
Getting no timeouts for all of my pings,
These are a few of my favourite things!

Reliable software that runs without crashes,
Packets on networks that avoid all the clashes,
Stars and big comets and  planets with rings,
These are a few of my favorite things!

When the segs fault!
When my apps freeze!
When I’m feeling sad!
I simply remember my favorite things,
And then I don’t feel so bad!

Ah, that did the trick. =)

Note to self: Don’t break into song during interview.

Recently, I had to do some work with a java Server program, that ran on my laptop. It acts like a very simplified server, so gets requests for files, finds it on the hard drive, and sends the response. I wanted to measure the server’s performance, so I used http_load, a program that sends out up to 62,000 simultaneous requests to an address, gets the response and gives you useful stats like mean bytes/connection, fetches/sec,  throughput, mean delay, etc…

My set up, was having the server running on my laptop, then making the request from any location on the interweb. This is where I ran into my problem, I am a Bell Sympatico ADSL subscriber, and connected to the internet via a Speedstream 6520 modem. The Speedstream acts like a router, so there’s an external IP seen to the world (the one we want), and an internal IP assigned to my laptop. The problem with this setup, is that if I feed http_load my external IP, all the requests wouldn’t be arriving on my laptop. It took me quite a bit of work, but here’s how I solved this problem. First some background info:

Router – Speedstream 6520
Server – Binded and listening on “localhost”
External IP – aa.bb.cc.dd
Internal IP – 192.168.2.10
Localhost – 127.0.0.1

So the first problem is getting the requests going to the External IP to actually reach the Internal IP (which is the one your computer has). To actually get this to happen, we must actually set up the router to do “port forwarding“. What port forwarding means, is any requests that come to aa.bb.cc.dd on port 1337 (aa.bb.cc.dd:1337), we take those requests and just pass it along directly to a specified Internal IP. You have to be thorough! So don’t forget to forward requests for BOTH TCP and UDP! Each router is different, so just look up the manual for your router and it shoudl contain instructions on how to forward IP.

Okay, so now everything is being forwarded to 127.168.2.10, but we’re not done yet. My server is binded to localhost- 127.0.0.1 – and the requests are coming into 127.168.2.10. So what we gotta do now is get those requests to come to 127.0.0.1. We do this by messing around with the hosts file.

Every OS has a hosts file. The hosts file is actually the same one used in old-school DNS servers, which is a list of addresses, with the IP it should be going to. In there, you will find “localhost” with a specified IP of 127.0.0.1 (which is how your computer KNOWS what the value of local host is… you can do a nice prank on someone, by specifying their favourite site as another IP). You then add a new entry:

127.0.0.1     192.168.2.10

Which tells the os, “if anyone tries to access 192.168.2.10, give them localhost instead!” Which is what we want! Now our server that’s sitting there patiently on 127.0.0.1, will actually get the requests from the interwebs and be able to send back a response!

One drawback. As I mentioned before, I’m using Bell Sympatico ADSL. ADSL is asynchronous DSL, which means the download and upload rates are different. Download rates tend to be VASTLY higher then upload rates, due to the fact that for more common web tasks, uploads will be minimal (usually just requests for pages). So running a server on this connection will give you an extremely slow server. But hey, it works!

I started doing sudoku in 2005. It was usually in the paper, and I was bored, so I decided to give it a try. I became hooked. As I became more obsessed, I began to wonder to myself, if I could find a way to look at a sudoku problem, and solve it instantly. I thought it was possible, because it has the following properties:

• A sudoku puzzle is an nxn matrix (square)
• All columns and rows add up to the same number: 45
• It is a latin square

So I started trying all sorts of things, to see if a method existed to solve it. I even wrote a guide on how to solve it by pen and paper. Exasperated, I went and talked to my math professor. He told me point-blank, “boy, its not possible, but if you can figure out a way to do it, you’ll be a millionaire!” You see, the problem of solving a sudoku problem is NP-Complete.

Let me explain a little bit about NP-complete problems. They are a type of problem who’s answer can be checked and verified very quickly, but actually coming up with that answer would take quite a long time (I know, I know, deterministic Turing machine, but that would require 2 more definitions and like 4 more paragraphs!) There’s another set of problems that are “Polynomial”, meaning they CAN be solved fairly quickly. All the NP-complete problems are linked to one another, so if you can figure out how to do one in Poly-time, then you can do them all in Poly-time.  However, if you do manage to figure out that algorithm, then you’ve essentially solved the “P vs NP” problem, a “Millennium Prize” problem, netting you $1 million.

So imagine my surprise today, upon reading the Toronto Star, and seeing that an “academic finally cracks the Sudoku code“! I didn’t really believe it, so I checked out the paper. Here’s the algorithm:

1. Find all forced numbers in the puzzle
2. Mark up the puzzle
3. Search iteratively for preemptive sets in all rows, columns, and boxes, taking appropriate crossout action as each new preemptive set is discovered -until
4. either
   a) a solution is found or
   b) a random choice must be made for continuation
5. If 4a), then end; if 4b), then go to step 3.

This is actually the same algorithm I use when I am doing it myself. So, let me reword it for you:

1. Find all the obvious ones (forced, meaning those numbers can go no where else)
2. Now in each square, list all the possible numbers that can go there and write it in that box (the mark ups)
3. Look at the entire puzzle, go through the mark ups, and see which ones cancel each other out. Do this until
4. You end up with squares with only one mark up left (thus it must be the solution) or squares where you have to guess (usually two choices).
5. If there’s only one mark up, that’s the solution. Else, go back to step 3.

If you ever played Nintendo’s Brain Age, their game allows you to use the same system of “markups”, so really, the algorithm is just what people would be doing anyways:

Ram Murty, a Queen’s University mathematics professor who has read the paper – “Pen-and-Paper Algorithm for Solving Sudoku puzzles” – said Crook has “codified what the average mind does when it looks at a Sudoku problem.”

The algorithm doesn’t even do anything to solve the “P vs NP” problem, since this is just a sudoku puzzle of size 9×9. Once you move to bigger ones, it takes longer and longer, which defeats the purpose!  As well, the article brags that the “Sudoku Code” has been cracked, despite the existence of other algorithms to solve sudoku.

I got bored of sudoku a while back, but maybe I’ll try to program a sudoku-solver. Sounds fun.

On Wednesday, March 18th, 2009, my laptop-loving decided it simply didn’t want to live in this world anymore. A world where it had to co-exist with ubuntu, macs, open-source, and all sorts of competition. So what did it do? It decided just stop working. Here’s what happened.

I booted up my PC and vista loaded fine. So I start running a few applications, browse around a bit, checked my email. Well, tried to check it. You see, that’s when my computer decided to freeze.

So I shrug it off, restart my computer, same sequence. It freezes again. And again. And again. I try all different kinds of combinations, but nothing works, it just freezes for no apparent reason! I have tons of experience fixing pcs, I even used work in the RMA department (fixing defective pcs and shipping it back to the customer), but I’ve never worked with vista machines before, so this was a good learning experience.

If your computer freezes for no apparent reason, you want to try and find out if its an infection issue, a hardware issue, or a software issue. To do this, its usually a good bet to get into safe mode. In safe mode, only the minimal of processes are running, so if there was a bad program running around, its a good bet you’ll find it here.

To get into safe mode, repeatedly  tap F8 while your computer is booting, preferably before vista starts to load, and you will get the following menu:

• Safe Mode
  
• Safe Mode with Networking
  
• Safe Mode with Command Prompt
• Enable Boot Logging
  
• Enable low-resolution video (640×480)
  
• Last Known Good Configuration (advanced)
  
• Directory Services Restore Mode
  
• Debugging Mode
  
• Disable automatic restart on system failure
  
• Disable Driver Signature Enforcement
• Repair Your Computer
  
• Start Windows Normally
  

Safe mode works fine. No freezes at all. Safe mode with networking freezes. So this is where I start attacking. I disable services, stop processes from starting up, update drivers, roll back drivers, etc… but nothing works, it still freezes. So I decide to try the “repair your computer” option.

I have a dell xps 1350, so its just the stuff on the recovery drive. Unfortunately, their utilies are somewhat “hard-coded”, meaning they make too many assumptions, which is not good for my system; dual-boot ubuntu + vista. However, I dug around a bit, and found the Factory image (Factory.wim)! So how to apply it? You can use imagex. Imagex is a command-line tool that lets you make images or apply images.

Imagex is included in the Windows Automated Installation Kit (WAIK), which is a heft 1 GB download. I decide to give it a go, but the windows site wouldn’t let me download! The validator wouldn’t validate my valid version of vindows (sorry!) vista!

Turns out, imagex only needs the following files to run:

• imagex.exe
• intlcfg.exe
• wimfltr.inf
• wimfltr.sys
• wimgapi.dll

Which I was able to find. I won’t say where I found it. So you have to look for it on your own. Once you legally obtain the files, you install it by right-clicking “wimfltr.inf”, then click on “install”. Its not a true install (won’t be in your PATH or anything), so you probably have to navigate to imagex’s location to run it. Here’s how you use it:

IMAGEX.exe /apply [Directory:\Location_of_Factory.wim\ 1 [WindowsInstallationDirectory]

And it will apply the image. This worked great, and my laptop was restored back to factory settings. A clean slate. So I’m really happy now, reinstalling old applications, setting things up again, then it freezes. This is bad. So I restart my computer, and now it doesn’t even boot. It gets stuck loading crcdisk.sys.

So it didn’t work out, but I learnt a lot about fixing Vista Machines. So at least I got something out of this whole ordeal.

Some exciting news happened today. As you may or may not know, I’m a TA for CSCD08, a software engineering course at UTSC. Its pretty much one of the BEST courses you can take, as a computer science student at UTSC. Why? Because you actually get to make something. All through your undergrad, you pretty do simple little programs, like “linked list”, or “binary sort tree”. In d08, you get to build something big, with a team, something that could actually be used in the industry.

When I did the course last year, I had to build an online photo editor. This was actually before photoshop express came out and destroyed the competition. There were four teams, and only two of them (mine included) decided to use a framework. We built it using a LAMP stack, with django as our web framework, and dojo as our javascript framework.  My team and I were actually able to do a pretty good job. It was even better then the best online photo editor available at the time.

So imagine my enthusiam, at being able to TA the course this year. The professor and I discussed a few new projects for the students to do, and he had actually managed to find Live TTC Tracking Data! So the project this year, was to use the Live TTC Tracking Data to create an online application, to help predict when busses would arrive at each stop.

The students completed their projects 2 weeks ago, and just today, it exploded. We contacted TTC about our project, and the next thing we know, nextbus (the source of the live TTC tracking data) released their version! This really excited the d08 students, so next thing we know, the entire class starts advertising and broadcasting their projects through the internet! I think Twitter was the funnest one. 6 new guys signed up for twitter, and started broadcasting it:

Which is pretty awesome! My favourite response however, was this one:

We’ve been tracking the visitors for every site, and it appears that citytv have been visiting it, even nextbus themselves in california. So hopefully it will bode well.

I guess that’s what makes d08 so awesome. Applications that are cutting edge, and can actually compete with real-world applications.

When my year did it, photoshop express came out 2 months later and slaughtered the competition. But this year? It appears my students are already ahead of the curve. Good luck guys!