[Haskell-cafe] An interesting toy

[Ryan Dickie]

Sounds like a neat program. I'm on a laptop right now but i'll check it out
later.
The reason I am mailling is because you can use mencoder to convert a stream
of image files into a video file.

http://www.mplayerhq.hu/DOCS/HTML/en/menc-feat-enc-images.html

--ryan

On 5/5/07, Andrew Coppin <andrewcoppin at btinternet.com> wrote:
>
>  Greetings.
>
> I have something which you might find mildly interesting. (Please don't
> attempt the following unless you have some serious CPU power available, and
> several hundred MB of hard drive space free.)
>
>   darcs get http://www.orphi.me.uk/darcs/Chaos
>   cd Chaos
>   ghc -O2 --make System1
>   ./System1
>
> On my super-hyper-monster machine, the program takes an entire 15 minutes
> to run to completion. When it's done, you should have 500 images sitting in
> front of you. (They're in PPM format - hence the several hundred MB of disk
> space!) The images are the frames that make up an animation; if you can find
> a way to "play" this animation, you'll be treated to a truely psychedelic
> light show! (If not then you'll just have to admire them one at a time. The
> first few dozen frames are quite boring by the way...)
>
> If you want to, you can change the image size. For example, "./System1
> 800" will render at 800x800 pixels instead of the default 200x200. (Be
> prepaired for *big* slowdowns!)
>
> *What is it?*
>
> Well, it's a physical simulation of a "chaos pendulum". That is, a
> magnetic pendulum suspended over a set of magnets. The pendulum would just
> swing back and forth, but the magnets perturb its path in complex and
> unpredictable ways.
>
> However, rather than simulate just 1 pendulum, the program simulates
> 40,000 of them, all at once! For each pixel, a pendulum is initialised with
> a velocity of zero and an initial position corresponding to the pixel
> coordinates. As the pendulums swing, each pixel is coloured according to the
> proximity of the corresponding pendulum to the tree magnets.
>
> *Help requested...*
>
> Can anybody tell me how to make the program go faster?
>
> I already replaced all the lists with IOUArrays, which resulted in big,
> big speedups (and a large decrease in memory usage). But I don't know how to
> make it go any faster. I find it worrying that the process of converting
> pendulum positions to colours appears to take significantly longer than the
> much more complex task of performing the numerical integration to discover
> the new pendulum positions. Indeed, using GHC's profiling tools indicates
> that the most time is spent executing the function "quant8". This function
> is defined as:
>
>   quant8 :: Double -> Word8
>   quant8 = floor . (0xFF *)
>
> I can't begin to *imagine* how *this* can be the most compute-intensive
> part of the program when I've got all sorts of heavy metal maths going on
> with the numerical integration and so forth...! Anyway, if anybody can tell
> me how to make it run faster, I'd be most appriciative!
>
> Also, is there an easy way to make the program use *both* of the CPUs in
> my PC? (Given that the program maps two functions over two big IOUArrays...)
>
> Finally, if anybody has any random comments about the [lack of] qualify in
> my source code, feel free...
>
>
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