My goal was to be able to record finger gestures and then detect them when a user makes these gestures. I had 2 goals in mind – no OpenCV (i.e. I will use just depth data) and no wearing special stuff to guide anything.

So, let us see what I did. Basically, I used the CandescentNUI Hand Tracker to get a collection of fingertip locations and points and then applied two techniques to try and recognize the gestures we make.

First, I tried using the Passive-Aggressive algorithm by Crammer et. al. This algorithm uses an online-learning approach to build a hyperplane (in 3 dimensions, this is a plane, in 2 dimensions – a line etc. Basically, this is what is defined when you try to define a “surface” like structure for a space. Take 2 non-parallel vectors in 3D space and you can construct the entirety of the 2D world. The hyperplane is just that – an entire space (a subspace with 1 dim less than the one we are operating in).

The hyperplane is supposed to act like a brick wall (if we’re in 3D – no point visualizing a higher dimension). When we see a new data point come in, we want to inspect on which side of the wall it lies and then we can “detect” or label this point. This is the binary classifier.

The dataset consists of raw point coordinates in the space of the human palm seen by the kinect. Now it turns out that the online passive-aggressive algorithm fails at constructing a decent hyperplane separating 2 classes (data points for 2 different gestures).

The obvious hack was to deploy a nearest neighbors classifier. The trick I used was that I ran a large cluster k-means on the data and built myself a dataset consisting entirely of cluster centers. So I was able to reduce the neighbors tenfold and still get fantastic performance. A simple technique worked fabulously in this situation and I couldn’t be more pleased.

Here is a video of the gesture-detector in action. The annotations should show you what to look @

The source is up on github. The code is very kludgy and I will fix it up after finals week. In case you’re in a hurry : http://github.com/shriphani/KinectSpell 

Now, it is time to try and avoid failing in the finals x(.

Reductions were (I am using the past tense since I haven’t picked such problems up in the recent past) central to proving NP Completeness. One of the rather interesting pitfalls undergrads @ Purdue seem to be facing is in understanding the reduction process.

In particular, I could boil their confusion down to something like this:

I know something about problem “a” (in this case, “a” is NP-Complete). So, if I need to figure something out about the NP-Completeness of some problem “b”, I will make a sincere effort to solve it using “a”. If I solve it using “a”, “b” is NP-Complete.

WRONG! I am a math major and I see the temptation to use a known problem’s solution to make some inferences about an unknown problem but seriously that is not what you are looking for here.

The fail in this approach is that no one is able to grasp the correct trail of thought. This is how you think:

I have some information about the perf of a, let me use that to make some inferences about b.

How do you infer stuff about b using a?

Let us say we are faced with the following problem:

You are sitting in level 1 of the Lawson CS Building. Your goal is to go to the basement.
Last week, you figured out:

• How to get to Level 2 from Level 1 (takes 2 minutes)
• How to get from Level 1 to the basement.  (takes 4 minutes)

So, here’s a diagram and a problem description:

To be solved: Get to basement from level 1

What we know: Getting to level 2 from level 1 (takes 2 minutes), Getting to basement from level 2 (takes 4 minutes)

So, if you apply the ass-backwards thinking that most people seem to do, we would go from level 1 to level 2 and then go to the basement from there in a grand total of 6 minutes.

Ok, what then? Well, using the problem solving structure you were applying before, you ended up concluding that going from level 1 to the basement will take 6 minutes (just like how you concluded that b is now NP-Complete).

But that is dead wrong. From what we see, the path you choose to solving a problem tells you nothing about how easily the problem can be solved!
When you chose to solve “b” using “a”, you made a (potentially stupid) choice about how to solve “b”. Possibly “b” could have a polynomial time solution and you still chose to apply a solution to it that won’t finish till your grandkids are born.

Here is how you approach that problem:

• You know something about “a”. More precisely, you know “a” is NP-Complete. You know that there is no polynomial time algorithm known for “a”.
• You then decide, “Hey, let me see if I can solve “a” using “b”.
• If you figure out you can solve “a” using “b”, then obviously, the theoretical lower bound you computed for “a”, holds for “b”.  You now know that “b” cannot do better than “a” (if it did, you might have proved P = NP :)).
• Well, now we know that since “b” cannot do better than “a”, “b” is NP-Complete    (You still need to prove that “b” is in NP but I am assuming you know how to do that)

That wasn’t so hard, was it?

Some salient features of Scheme code I’ve written so far (not features of scheme but shit “I” do with it):

• Aggressive use of map-reduce. I found this too sexy, I use it everywhere.
• If it compiles, it is most definitely correct (at least I’ve never had runtime fuck-ups happen to me – this is pretty nice since with some thinking I could accomplish quite a lot in scheme).
• I have very aggressively used lambdas.

Keeping these new habits in mind, I sat down to tackle a p-set yesterday and finished in no time. I then was unable to comprehend the reason why I was so slow compared to the demo of his own solution (I was implementing the arc-consistency heuristic to solve n-queens). Upon investigation, I saw rubbish like this in my code:

Well foo-that-returns array was supposed to return a subset of values that satisfied a proposition (from an original finite domain). I totally carried over my rubbish habits from other prog languages ([] is #f and [...] is #t so I will continue to use those) rather than doing:

This looks a lot better and it was a lot faster. My reasoning for this speed improvement is that I just obtained a rather large array, checked for emptiness and then threw it away causing the scheme GC to kick in. Using some makes it look a lot more like a quantifier which is precisely how this procedure must be written. This summer, I really need to rock SICP and fix my shoddy half-knowledge situation with regards to functional programming.

Besides that, my research seemed to hit a roadblock close to the end of this semester when a sudden miracle (and a reddit-browsing approach to lit. search) led me to fix things so I can still declare victory. I will not post more about my work since I am applying the Mao approach (is it even Mao? I don’t know) – “Keep your head low and rise to the top, then the world will take notice”. I have a bad habit of gloating after I post stuff here, it is best if I only put materials here after I finish (and hopefully produce a sexy paper).

Anyway, more posts (better in quality than this) to follow.

• Due to some total n00b carelessness on my part, my trip to home (Singapore) got cancelled one day before I was scheduled to fly and one week later, I am in my homeland, India (funny how that worked out).
• My Macbook Pro HD died completing a long list of problems with the machine. In its current state, the DVD drive refuses to work, the laptop hates Direct Current, HD is dead and screen has a few dead pixels on it. I am not interested in investing any $$ on this machine and considering that it is not even under warranty, I decided to make the plunge into the dell world and get a machine that would perform well for the next 6 years (XPS does offer good value for money).

Also, I really like this new theme on my blog – it is simple and without rubbish and I think this is what I want – for content to take center-stage.

More bad news: I cannot code over the break since I do not have access to a computer with a text editor and compilers / interpreters whatever. Brilliant. But maybe this is a good thing. I can really recharge my batteries now (whatever that means).

Now, it is time to gear up for a CS 497 project (got to finalize things first) and some interesting coursework (not the bogus BS I did last sem).

Anywho my coursework for next sem is lined up in the following fashion:

• ECE 473 (Machine Learning)
• CS 497 (Honors research)
• CS 448 (Theory of relational databases)
• MA 358 (Logic)
• Phys 221 (Optics and E&M – I have put this sucker off for so long I almost feel guilty about it)

Hopefully things will go well and my brain will flourish in the relatively more interesting (compared to previous semesters) coursework.

Oh by the way, my new GPA is 3.94 (fuck yeah! an increase by a hundredth). Some interesting stuff I learned:

• Panini was not an asshole (I really thought he existed to piss people off in a grade 6 history lesson on Indian literature).
• I am really not prepared for the GRE :(.

OK OK, the GRE situation – I just do not like it. The verbal section just seems to be designed to piss people off – no really. I mean I have to pick up a book and master vocabulary so I can impress who? Nobody – that’s right. If someone were to test me on my SAT vocabulary 48 hours I took the test, I would have flunked – absolutely flunked.

Anyway, this is life – we are supposed to suffer for bad decisions made by us and everyone else, and we are supposed to enjoy the fruits of good decisions made by just us. Not fair.

The trip was extremely informative as this was the first time I got to see such talent (inb4 LOL MS). And boy were the problems beautiful. At one point I hacked up a solution by cheating (I analyzed the time using the recursion tree and figured out a solution). The interviewer seemed amused by the solution!!

And guess what:

I GOT IN !

Also, this is probably the first “thing” I have achieved in a long time so that was one of the positives. I guess I will be in Washington in the Summer.

Another positive coming out of my research – our poster in the Kihara laboratory gets to be displayed in GIW 2010.

Now, it is time to get pwned in the finals. Incompetence, unethical behavior by nutters who call me a friend have been very harsh on my performance this semester and have severely affected my final exam situation (i.e. no fucking time to prepare – thank you “teammates”).

I only hope I can keep the good news coming in and not have to suffer at the hands of the super-parasite types in the CS department at Purdue (this rant merits its own post and there is one coming).

And of course, more people (millions) know about that app than about mine (about 20). Hmm no fair.

So this semester I am really looking forward to my compilers class, the last portion of my numerical methods class and of course my CS 490 project with Dr. Kihara and of course I want to achieve my goal of being able to watch anime without having to read subtitles.

This would also be one of the only semesters where a book for which I paid $30 on amazon looks like it was printed by one of those shady book-vendors in the streets of Hyderabad. Seriously the book by Skeele is printed on paper that is coarse and it just doesn’t look like a decent textbook. I also do not agree with the style of the book and since I used LaTeX over the summer, the pictures and the text look like they have just been thrown together. It just doesn’t look right.

Anyway, I hope this semester goes well.

• CS 352 – Compilers (supposed to be hard)
• CS 314 – Numerical Methods (this course looked very interesting).
• MA 375 – Discrete Math (to consolidate my probability concepts and to study graphs deeply)
• COM 217 – Had to take it sometime.
• CS 490 – Bioinformatics independent study.

So, I chickened out of ECE 270 since Compilers + Digital Systems would be suicide and since CS 497 is planned for semester #6, I am in a tight spot since one more CS course can cause my GPA in all courses to tank so I am stuck here with this stupid setup. Also, I took the Phy test out and I am not sure if that went very well so I will have to wait.

Anyway, enough about the current semester. Summer was the most eventful time of my 2 years here @ Purdue. First, I worked for Dr. David S. Ebert in his Visualization laboratory (PURPL) on an emergency response system (the project screenshots shown there are still old. They probably won’t be updated in a while). It was extremely interesting since I got to work with OpenGL (I am not sure I will ever get a chance to work with it again) and got to learn about computer graphics. Here is a list of things we got done in the summer:

• A 3D picking algorithm (nothing too fancy. This took a while since I had to read OpenGL documentation about their coordinate systems).
• A controllable camera (one you can turn, zoom in/out with using keystrokes)
• A couple of camera angles (The high angle mode and the first person mode). Getting them to follow characters smoothly was a crazy issue.
• Then we implemented a path based attribute visualization technique which became the topic for my poster.

I stood with a poster @ the SURF symposium and I won “Top Poster” and my grad mentor, S. Kim, earned “Graduate Student Mentor of the Summer” so I would rate my SURF 2010 experience as one of the top 10 experiences of my life (the other 9 are yet to arrive).

Now, I might just go and join SIG-APP or something like that to spend spare time. Now, here are some goals I set for myself this semester:

• Prepare for the GRE (it sucks but it has to be done).
• Learn how to speak Japanese reasonably well.
• Consolidate my probability knowledge (I would really like to learn it well this time round).
• Finish reading a book on NP Complete problems.

Well, I just hope I don’t screw up anything this year since this is my last chance to build a great resume for grad school (and achieve some lofty goals which are too childish for even this blog) before applications season begins.

This concern is valid. Like most educated people, I have lost faith in modern journalism. India has generated a news channel ecosystem that dedicates solid portions of a day to exploring thought-provoking concepts like the afterlife, asks the leader of India’s neighbor (Pakistan) if surgical strikes by the Indian army on Pakistani soil would lead to war (I mean seriously, do you not know what sovereignty is?), spends time exploring conspiracy theories and here’s the kicker – engages in irritating nationalist worship. No, really. Since 2005, every article about Indians has had one tune: How rich Indians owning companies started by their grandparents, able to achieve monopolies in India through bribery, corruption and other questionable activities, are acquiring companies abroad and hence putting us on the world map.(nothing reeks of underdog behavior more than stating every Indian achievement as an assertion of our geographical boundaries) Every year we learn about Bollywood showing its power (they make movies. Why is it admirable if they can pull strings?).And every game India plays against Australia is about 24+ aged men troubled by Aussie mind games. They are fucking adult men. They don’t need you to defend them because they are just as big dickwads as anyone else who is playing the game.

The Indian media is a fucking joke. I guess this is the curse of 24 hour news. You hire people to generate so much crap 364 days in a year to fill 24 hours of every one of those days that on the one day something important happens, you have the collective journalistic capability and insight of a mediocre high school graduate.

Don’t agree with me? Monopolies and oligopolies are the biggest curse you can heap on an industry. Yet, all of India’s most powerful industrialists are the media’s darlings. The BCCI has been glorified by the media for the power it wields over the cricket world. Yet this one organization is responsible for the future of India’s most popular sport. We are a nation of 1 billion. We cannot generate opportunities for such a large population through one organization that conducts 2 domestic leagues. This organization is so caught up with its lucrative ventures that the Indian team is guaranteed to be tired before any major event thus putting our chances of winning the world cup at a severe risk. The BCCI is bad for the nation. The media doesn’t even question its monopoly status and its aggressive behavior towards any players who participate in a non-BCCI-blessed league.

And of course I read this economic times masterpiece: http://economictimes.indiatimes.com/features/the-sunday-et/people/Its-time-we-beat-the-West-let-the-East-rise/articleshow/5681401.cms

The headline of the fucking story is, “It’s time we beat the West & let the East rise”. Really? Here’s  a 2-bit manufacturer no-one knows anything about and he uses his only marketing avenue to speak about how he is the soldier in a war against a civilization. And the paper which is the “exclusive” marketing avenue (self-proclaimed) has reporters and editors with the IQ to publish this article. The kicker is that product will first launch in the United States. How is that for building goodwill?

Gandhi achieved what he did because he ensured that the injustice he faced did not go unnoticed. He took the blows and then ensured that this went on record and that the world got to see it. Non-violent protest itself wasn’t a powerful tool. It needed journalism from an unbiased organization to achieve its goals since this gave credibility to the protesters’ cause. To combat non-violent protest, the oppressors had to adopt methods outside the legal system and it would be hard to pull this off quietly if you attracted the media’s attention.

I do not believe that our media is capable of assisting another Gandhi, if a situation ever calls for an individual to assume a role similar to his in India’s struggle for her independence.