The Fourier transform of Lindy Hop, part II (the lead and the follow)

dnquark · 2 months

Don't know if grand-parent posts receive reply notifications, so here it goes again (if you are curious about the data):

I'm a little swamped right now, so I'm making the analysis code and the data public as is -- with no comments and some quick-and-dirty scripts in place of proper functions. However, the analysis workflow is documented in dance-science.org. The code is here: https://github.com/leoalekseyev/dancelab-analysis

The data for the original video is here: http://dl.dropbox.com/u/2685883/dancedata.tgz

dnquark · 2 months

I'm a little swamped right now, so I'm making the analysis code and the data public as is -- with no comments and some quick-and-dirty scripts in place of proper functions. However, the analysis workflow is documented in dance-science.org. The code is here: https://github.com/leoalekseyev/dancelab-analysis

The data for the original video is here: http://dl.dropbox.com/u/2685883/dancedata.tgz

dnquark · 2 months

Well, the full data set has acceleration in all 3 dimensions. However, at first glance, it seems that the lateral acceleration is almost perfectly correlated with the vertical one.

Another thing that's kind of cool is that for a while I thought that the data stream was ahead of the video. Then I watched very carefully and in slow motion, and I realized that it just looks this way, since we "wind up" for every move -- e.g., if I am standing still and then start a swingout, the first peak you'll see is going to be the bounce on 8, not the rock step on 1.

I have the data, and I'll post it if people are curious. Right now my priority is to streamline the analysis -- my current Matlab code is too embarrassing to post; once I fix that, I'll make it public.

dnquark · 2 months

If you liked my previous Lindy Hop Fourier transform video, you'll love this one. Better dancing, better data, and better video quality! You can see the lead's and the follow's acceleration traces overlaid together, and the video includes the follow's angular velocity data (check out the graph of her swivels!)

dnquark · 2 months

The data on the left is from the accelerometer in my pocket (top trace). The bottom two traces are the frequency spectrum of the data. Fourier transforms allow you to go between time representation and frequency representation. For instance, if you played an A on an instrument and then looked directly at the data collected by the microphone, you'd see that the numbers form a periodic pattern, a wave at frequency 440 Hz. If you were then to take a Fourier transform, you'd see a signal that's mostly zero with a sharp spike at 440 Hz, because that's the frequency content of the signal. Likewise, here you see a sharp spike at 161 bpm because my motion always has a bounce that's in time with the 161 bpm song.

tmalsburg2 · 2 months

I found Speedbar utterly useless without ECB, which is somewhat unfortunate, because I would prefer a minimialistic solution. I can't for the life of me figure out how to make Speedbar display function or method names, or tags for that matter. I there are any recipes and how-tos, I'd love to see them...

dnquark · 3 months

If there are more Evil users in /r/emacs, please share your favorite tricks!

dnquark · 3 months

Put together, spoken over, video synced with the audio. I wish I could write and talk this fast in real time :)

dnquark · 3 months

An older Fujitsu T4410... Works well enough, although I'm jealous of people with Thinkpad tablets.

dnquark · 3 months

Aww, multivariable calc is useful :) But multivariable stuff isn't very important in understanding this derivation... a double integral is kind of like a single integral, just over a function defined in 2 or 3 or N dimensions. The concept that's kind of important though is switching between cartesian and polar coordinates. Anyway, after you are exposed to this stuff a little more, you'll see that it's not very hard :)

dnquark · 3 months

You realize that the video was sped up to match the audio, right? :P

dnquark · 3 months

Good call on the audio; I haven't been entirely happy with the background noise / sibilant S's / lack of consistency b/w recording "sessions", so any tips are definitely welcome. (It doesn't help that I'm using a cheap-o headset.)

Re: software -- I am simply using Xournal on a tablet PC (or, rather, my own fork with image support and some other niceties: https://github.com/leoalekseyev/xournal). If I keep making these videos, I'll have to implement some more convenience features :)

mortiferus · 3 months

This is an awesome mode and you guys should promote it more. One thing that threw me off is that I needed to modify the equations in some form (like, insert and delete a space) before the font lock registered.

There's one mis-design that ought to be fixed at some point: the underscores in labels and citations get turned into subscripts, which is annoying. At the very least, there should be a switch to turn off the subscript handling, since AuCTEX already provides some subscript/superscript handling.

gislikarl · 3 months

Not related to learning Emacs per se, but I would recommend this to anyone new: https://github.com/technomancy/emacs-starter-kit

IMHO Emacs defaults are not beginner-friendly, at all. Ido mode, etc make life much easier!

dnquark · 3 months

So what I ended up doing was:

Create a draft/outline of the presentation, highlight the talking points
Write out the slides while recording the screen
Narrate the existing slides
Edit the video to go with the narration by appropriately speeding up or pausing some segments, and cutting out others.

Altogether it's kind of involved to do it in separate steps, but the net benefit is that the final result doesn't waste time. The video was 5.5 minutes; I estimate that a classroom presentation of the same material with stuff being written on the board would take at least 15 minutes.

dnquark · 4 months

I mostly explored the consequences of the hyperbolic dispersion for applications in imaging and waveguiding, and provided theoretical models for two groups doing proof-of-principle experiments. My exact research was much too technical to be included in the video :)

I should note, though, that the current understanding / interpretation of hyperbolic materials was evolving throughout the time I was in grad school. For instance, when I started, we weren't at all focusing on the hyperbolic nature of the dispersion, but it soon became clear that it is the most useful way to think of such materials. This understanding came in the course of my research (and that of other groups in the field). Thus, it is hard for me to conceptually separate the general description of hyperbolic media from the exact details of my work.

dnquark · 4 months

If you thought that was fast, you should've seen my "draft" version :)

In terms of the optimal duration of the video: it's an interesting question, and it depends entirely on the audience. If someone doesn't care about the subject, they won't watch for even a minute. If someone is really interested, they can watch for 20 minutes. I feel that the vast majority of people fall into the "kind of care" category. I hypothesized that 5 minutes was a good target duration for this audience. An ideal (but time-consuming) solution would be to produce both a "lightning" version and a "virtual TED talk version".

Yes, there are some examples of hyperbolic behavior in nature, but they are a bit exotic, and exist typically in the mid-to-far IR (or even THz) in a narrow frequency band. Examples include bismuth at 50 micron wavelengths and sapphire around 20 microns.

dnquark · 4 months

They could be very interesting for broadband energy absorption (see e.g. http://www.physorg.com/news/2011-09-darker-than-black-metamaterial-efficient-solar-cells.html)

dnquark · 4 months

I can't think of a particular utility. The gap does mean that propagation is forbidden for wavevectors that are smaller in magnitude than the gap (or that aren't appropriately oriented), but I can't think of a killer app for this :)

dnquark · 4 months

This is Xournal, the awesome open-source PDF annotation / inking app (actually, this is my fork of it that includes quite a few more features.)

Btw, evanescent waves are, technically, hyperbolic -- that is, the dispersion relation is a hyperbola. Unfortunately, that's not very useful since when k becomes large, they die exponentially quickly.

dnquark

TROPHY CASE

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