Rigid Body Motion

Posted by on May 30, 2010 2 comments

Last week I had to give a presentation about Rigid Body Motion (ie the basics of rigid body physics and some general mechanics).

Here are two versions of my presentation (one with less text and one with more):

Rigid Body Motion Presentation as PPTX; Rigid Body Motion Presentation as PDF
Rigid Body Motion Full Version as PPTM; Rigid Body Motion Full Version as PDF

If you are truly interested in learning about rigid body physics, here are some books/links:

Cheers,
Andreas

PowerPoint LaTeX

Posted by on May 30, 2010 1 comment

Hey everybody :-)
I only wanted to point out that I've uploaded a new and improved version of PowerPoint LaTeX at http://code.google.com/p/powerpointtools/ - it now supports MiKTeX \o/

I've also finally added a project page for it to this blog.
More updates might follow soon if I find enough spare time :-)
Cheers,
Andreas

A quick note on quantifiers: For almost all and there exist infinitely many

Posted by on March 27, 2010 No comments

It's been a while since my last post and now it's time for a mathematical post:

I'm currently preparing for a math exam (calculus) and I'm thinking it would be nice if there was a way to avoid much of the "for every \epsilon > 0 there is an N \in \mathbb{N}, so that for all n \ge N some property ... holds" stuff you find in textbooks. Some textbooks actually shorten it to "for every \epsilon > 0 some property ... holds for almost all n".
However, I haven't found a quantifier to express this anywhere yet, so I'm proposing to introduce a new one:

\tilde{\forall} x \in M: P(x) should mean "for almost all x \in M P(x) holds", which suggests that there are only finitely many elements for which it does not hold.
One can formalize this as:
\tilde{\forall} x \in M: P(x) \equiv \exists n \in \mathbb{N}: \left | \left \{ x \in M \mid \neg P(x) \right \} \right | \le n

Of course, a new existential quantifier is required then, too (for negation):
\tilde{\exists} x \in M: P(x) stands for "there exist infinitely many x \in M, for which P(x) holds".
And this can be formalized as:
\tilde{\exists} x \in M: P(x) \equiv \forall n \in \mathbb{N}: \left | \left \{ x \in M \mid P(x) \right \} \right | > n

It's easy to see that \neg \left ( \tilde{\forall} x \in M: P(x) \right ) \equiv \tilde{\exists} x \in M: \neg P(x)

Thus one can use the two quantifiers just as one would use \forall and \exists usually. Note however than \forall and \tilde{\forall} don't interchange and neither do \exists and \tilde{\exists}.

One last note: it might be worth using a different notation, for example: \exists ^ \infty might be easier to understand than \tilde{\exists} , and \forall ^ \approx might be better than \tilde{\forall}.

I'll try to formalize these quantifiers some more when I find some spare time.

Stay tuned for coding related updates soon :-)
Cheers,
Andreas

Random Things

Posted by on November 27, 2009 No comments

It's been a while since the last update. Here's a small update on what I'm thinking about various stuff.

Prototype

Gameplay is okay I guess. Nothing I would spent too much time on though. It looks a lot worse than GTA 4 though (same as Crackdown).

Resident Evil

Seems to be lots of fun and some nice graphics, too.

Red Faction: Guerrilla

Some weird texture filtering issues and the presentation doesn't knock off my chair (terrain popping and other ugliness), but multiplayer is loads of fun with friends. Physics isn't completely stable though. I played the game for one hour in MP with friends and there were quite a few cases where geometry dropped through the floor with enough pressure from above (after destroying a building).

Brüno

A bad and quite stupid movie (Ali G in Da House is probably the only movie I kinda like that stars Cohen). If you haven't watched it already, don't >_<

Shadow Complex

I bought shadow complex a few weeks ago and I have to say that it is an awesome game. I read somewhere that the developer used the Metroid series as inspiration and it shows. It's really fun to play and quite addictive. The graphics are pretty awesome (it is using the Unreal 3 engine) and the whole presentation is pretty polished. It certainly is worth its 1200 gamerpoints

Summing Formulas

A month ago I was doing some exercises in an analysis book (Königsberger) and found a nice/interesting problem:

Prove that if we denote of the sum of the numbers 1 to n to the p-th power by S_n^p = 1^p + 2^p + ... + n^p , then the following equation by Pascal holds: (p+1) S_n^p + \binom{ p + 1 }{ 2 } S_n^{p-1} + \binom{ p + 1 }{ 3 } S_n^{p-2} + ... + S_n^0 = (n+1)^{p+1} - 1

It can be used to get recursively/iteratively get formulas for sums of higher powers of numbers.

This is interesting because the proof doesn't need any advanced maths (like eg the Euler-MacLaurin formula, which can be used to show this, too).

You can download the proof and a few examples here.

Cheers

Extracting Information from StudiVZ

Posted by on October 19, 2009 1 comment

Some time ago somebody stole 1 million data records from StudiVZ, the German Facebook clone. I'm not exactly sure why people call the person a hacker who stole data, because it appears he simply wrote a tool that harvested the publicly available data from StudiVZ (which everyone with an account can view).

People on StudiVZ share all their data by default---contrary to Facebook which values a person's private data a lot more. Thus by simply opening each profile from a dummy user and processing the HTML data from StudiVZ one can extract a lot and some more information from random people who probably don't even know about it or don't care.. so I'm not sure about the stealing part.

Apparently there are some captcha's when you start browsing searches beyond a few pages. I guess that is where the hacking part comes in, because getting around a captcha probably constitutes hacking---maybe?

Anyway I think part of the media coverage is a bit ridiculous because anyone can write a simple harvester in an hour or two. It took me one and half hours, so I think I'm on the safe side with this estimate and I didn't really have a clue about this stuff before either.

Since I don't want to "hack", I've only written a very tame harvester. It connects to your personal StudiVZ account, and retrieves the name and profile ID (and thus profile URL) of all your friends in the "Meine Freunde" pages.

It could do a lot more with that like retrieving everybody's birthday or random pictures, but I'm too lazy to code that because you use the same pattern for extracting data over and over again and it stops being interesting quite fast.

You can download the project here. It is a one file C# project. I'm releasing it under GPL (whatever).

It's really easy to explain how it works:

  • It uses System.Net's HttpWebRequest and HttpWebResponse to get (and post) web pages.
  • StudiVZ (like every other portal) uses cookies, so I create a CookieContainer and use it in every http request.
  • There are a few hidden values that StudiVZ expects during login. I'm retrieving them from the main page using custom built regular expressions. I've found a handy AJAX tester for .NET regular expressions. It was really useful for building the expressions and debugging them. (BTW you can find all URLs I used in the comments.)
  • After login I use the same pattern: get page & parse using regex for everything.
  • Visual Studio has an awesome "HTML Visualizer" for strings. It displays the content of a string as HTML page, which is really nifty if you're doing anything related to HTML processing.

The code is quite ugly. Well, it's not production code and this is only meant as a proof of concept.

Also note that I have at most violated the AGB of StudiVZ and not committed any criminal acts and I'm not planning to sell my friend's profile IDs or data either :-)

Maybe someone can extend the code and make it more useful. I guess it would be fun to automatically download all your pictures (including tags) and feed them into flickr or picasa... but someone else can do that.

Cheers,
Andreas

My Bachelor Thesis

Posted by on October 17, 2009 1 comment
Screenshot of Utah

Screenshot of Utah

For the last two months I have been working on my bachelor thesis at the Chair of Computer Graphics and Visualization. It is about "Multi-Tile Terrain Rendering with OGL/Equalizer"´.
The chair has a very nice Direct3D 10 terrain rendering engine and they want to run it at the newly founded KAUST (King Abdullah University of Science and Technology´) in a massive CAVE environment. A CAVE is a room whose walls are actually screens.
The CAVE at KAUST even supports stereoscopic rendering. Thus in total 12 views can be rendered to.

My job was to port said terrain engine from Direct3D to OpenGL and afterwards to the Equalizer framework, which is an open-source framework for parallelizing OpenGL applications.

You can find/download an online version of my bachelor thesis here. I'll upload the LaTeX at a later date and update this post.

I've spent the last months writing about all this, so I don't feel like talking about the thesis itself anymore. Instead the remainder of this post will contain a post-mortem of it.
Read more »

Sploidz Revisited (Unofficially)

Posted by on August 23, 2009 1 comment

I've already written about the semi-conductor project and how I've written some Flash animations/applications for it. Of course, I'm more interested in making fun stuff´, so I decided to put my knowledge to good use and write a small game to see how difficult/awkward Flash actually is.

To sum it up, it is somewhat awkward, at least if you use the IDE itself. FlashDevelop still is as nice as ever, but you can quickly develop games nonetheless. I prefer Torque Game Builder though in retrospect.

Before I continue talking about the development itself, let's take a look at the actual game. Sploidz was the first game I wrote using Torque Game Builder for Joshua Dallman, and since I still had all the assets in my subversion repository, it was an easy decision to try and port this game. If you want to play it, you can download it for free here.
I haven't ported everything: I've just rewritten the main characteristic features that make up Sploidz's code in ActionScript.

Without further ado´ here is the game:

Click to open Sploidz in its own window

Because the art is still copyrighted and I haven't heard back from Joshua yet ´, I decided to create a free version that only uses "coder art" - in this hand-drawn coder art :-)

Some´ have said that this version looks cuter, decide for yourself:

Click to open SploidzCC in its own window

Below you'll find a description of the development and at least one helpful trick and most importantly a link to the source code of the "copyright-free" version.

Because the orginal version is way too difficult to be really fun, I actually sat down one more time and added code to make the platform slower if you're in danger of losing (up to 3 times slower):

Click to open SploidzMoreFun in its own window

Read more »

More Book Reviews and re: Design Patterns

Posted by on August 18, 2009 No comments

Pattern-Oriented Software Architecture - A System of Patterns (PoSA I)

I've finally finished Pattern-Oriented Software Architecture - A System of Patterns and I want to say a few words about it.
First I don't think, it's a must-buy. It's okay to read (but more about that in a minute) and certainly it can come in handy to look up patterns while developing, but if you have small budget, it's better to get it from a library.

The book can be roughly divided into 4 parts: architectural patterns, design patterns, idioms, "trivia".

The chapter about architectural patterns is the most interesting,  where as the chapter about design patterns is okay, too, but also borrow or expands upon lots of concepts from the GoF book. The idioms chapter only contains one idiom (think small, language-specific "design pattern", e.g. reference counting in C++).
The "trivia" part contains information what pattern are, who came up with the idea, influences, the community, yada yada. The most interesting topic being the community and links in there.

The book itself is quite boring to read and the patterns are described in endless detail, which is good, if you want to look things up and avoid common mistakes. On the other hand this makes it a book, you should not read front to back, because it doesn't really make sense and you won't get a lot out of it either. (I actually read it front to back, and from that experience I draw my advice :-| ) Just skim over the patterns, until you find something you don't know and then read the paragraphs that are interesting until you think you understand the pattern and then read some more to verify that you really understand it, but you can probably skip 40% (or more) of the text, if you just want to learn about new patterns and not go into all the details.

Next I'll try to write a few words about each pattern (so I´ can look up the pattern here instead of in the book)´.

Note: I just found an awesome page, http://vico.org/pages/PatronsDisseny.html, that contains information about all patterns in the book, so it doesn't make sense for me to write about each and every one of them.

Architectural Patterns

  • Layers
  • Pipes and Filters
  • Blackboard
  • Broker
  • Model-View-Controller
  • Presentation-Abstraction-Control
  • Microkernel
  • Reflection

Design Patterns

  • Whole-Part
  • Master-Slave
  • Proxy
  • Command Processor
  • View Handler
  • Forwarder-Receiver
  • Client-Dispatcher-Server
  • Publisher-Subscriber

Idioms

  • Counted Pointer

Now that I'm done with this, I want to share a few useful resources mentioned in the book:

Personally idioms are very interesting for me, too, because the day-to-day coding work is in a specific language and idioms are exactly about that.
A little googling already turns up lots of useful sources. For example:

There are a few more pattern books that I plan to read, so let's see how that turns out..

A Manual for Writers of Research Papers, Theses, and Dissertations

This is an awesome book, that explains a lot about how to write research papers and also about all the little details you should pay attention, too. It's a good read - I spent 1.5 hours a day for a bit more than a week to read through it - and I think it's going to be quite useful, when I start writing my Bachelor Thesis in a few days.

I'm currently writing some ANTLR grammar and StringTemplate stuff and I might write something about that, too, on the weekend.
I'm not sure I'm really happy with ANTLR, but it's probably the best thing out there at the moment, but I'm totally in love with StringTemplate, even though you might say it has some rough edges, too.
But more on that on another day.

Over and otu,
Andreas

PowerPointLaTeX Update

Posted by on August 5, 2009 No comments

Because people complained to me about the formula feature in my PowerPointLaTeX add-in, which used a somewhat experimental approach to editing formula objects by adding an editing text shape that contained the formula code and that would be merged back into the formula as soon as you deselect it, I decided to rewrite it to use a standard modal dialog to edit formula objects:

PPTLaTeX_eqeditor

Updated Ribbon (above) and Formula Editor Dialog (below)

The editor isn't perfect (yet), but it certainly shouldn't add any bugs to the add-in and solve some natural issues the old approach created.

Implementation Note

The idea was pretty straight-forward but the actual UI design was a PITA due me not knowning the panel/flow/table layout concepts very well and the code still has some annoying quirks with auto-scroll, so I need to fix that later.

I almost rewrote the whole cache system, because I'm using a background thread for updating the preview (if the text is changed, a 500 msec timer is started which triggers an update) and the update accesses the cache system, which in turn accesses PowerPoint to return some data, which in turn is busy because of the modal dialog -> dead-lock.

The solution to this is very simple but was not obvious to me at first (I actually began to rewrite the cache system with a feeling that there should be an easier solution):
The background thread needs an Invoke call to update the preview picture because the control has been created by a different thread (the main thread) and the code to get an updated picture can simply be moved into Invoke delegate function.

This solved all my problems and made 4 hours of previous work and thinking about a new cache system obsolete :-|

Download the new build at: http://code.google.com/p/powerpointtools/downloads/list

Cheers,
Andreas

Semi-Conductor Optimization (Uni Project)

Posted by on August 2, 2009 No comments

I've written my last exam yesterday (except for two oral exams in September), so now I have got some spare time before I start working on my Bachelor Thesis tomorrow and I want to use it to wrap up a few things.

During this term I took part in a course that was both a (research) project/presentation/lecture thing, which was fun but also a lot of work.
I've already written about one mathematical aspect of it in my post about Analysis, Cauchy-Schwarz and Reciprocal Sums.

The project was about optimizing semi-conductor wiring placement. We wrote a small paper about our findings and the work it was based one - you can look download it here.

We also created a self-running presentation that doesn't contain any Maths at all but makes heavy use of Flash animations (which were exported to .gif manually, which was a huge pain in the ass, which I will never do again if possible) to visualize all the concepts and algorithms.

You can download a PowerPoint 2007 (.pptx) version here or one that works with PowerPoint 2003 here.

For the Student's I sat down and wrote a small Flash application to show the algorithms at work. It's not obvious how it works, so let me explain the major points:

  • On the right you have a number of panels that you can enlarge by clicking on the small button in the upper right of each panel.
  • The upper three panels show different views of the same dataset. They will all be updated as you run the algorithm step by step.
  • The fourth panel lets you change the number of wires and/or their activity.
  • The last panel shows the electrical field that is created by one active wire in the center. It was created using MatLAB. I've also uploaded the script here.

Abitag

Last but not least I've also uploaded the current version of all my .fla and .as files. You can download it here.

ActionScript is a nice language and you can quickly learn it using the available resources from Adobe.
While ActionScript 2.0 is arguably weird, ActionScript 3.0 is quite logical and it's syntax is straight-forward and consistent, too. You can't say that about the IDE (Flash CS4), which is braindead, but if you're only interested in writing ActionScript code, FlashDevelop is an excellent and free alternative.

This is it for now, maybe I'll play around with Flash some more another time.
Cheers,
Andreas

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