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# Week 309

I feel I've been neglecting the Azimuth Project a bit for the last week, so here's my apology and my plans for the future.

I've been talking about entropy, information theory and a bit of biology and economics with a group of people here — I call it the 'Entropy Club'. In the process I got distracted by 'Rényi entropy', an obscure idea from thermodynamics which, I'm happy to report, turned out to be an incredibly well-known idea in disguise: namely, free energy. I put a short paper about Rényi entropy on the arXiv and blogged about it, and the comments I got quickly led to dramatic improvements in the paper. It's a great example of how working online speeds up progress.

But now I want to do these things, roughly in this order:

• finish writing week309, about a Hopf bifurcation in a predator-prey model.

• write a blog post about 'Petri net field theory' - some work I'm doing with Jacob Biamonte, which applies quantum field theory and category theory to Petri nets. This overlaps a lot with week309, but I'll separate them out somehow.

• write the final blog post on Stabilization wedges.

On Friday I'm going to Angkor Wat for a week (it's right nearby), so I'll be quiet from the 18th to the 25th of February. I'll see how many of the above items I can do be Friday!

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1.

Have fun in Angkor Wat. It is certainly one of the most magnificent places I've ever been. We spent four solid days touring a small fraction of the different ancient temples. A week should be just about right. Siemreap is also a very nice little city. You should have fun. The people in Cambodia are very nice. The food is wonderful.

Comment Source:Have fun in Angkor Wat. It is certainly one of the most magnificent places I've ever been. We spent four solid days touring a small fraction of the different ancient temples. A week should be just about right. Siemreap is also a very nice little city. You should have fun. The people in Cambodia are very nice. The food is wonderful.
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2.
edited February 2011

This describes an example of state-of the-art ecological theory: Theoretical ecology: Waltz of the weevil, Nature 470, 47–49 (03 February 2011) doi:10.1038/470047a

You might like to mention it in week 309. I think it's an example of stochastic resonance. Certainly it uses a stochastic differential equation and other things that have been mentioned here. Quote:

Modern time-series analysis came to the rescue. Theoretical ecologists are familiar with the contributions of one of the authors (Ives) to ecological time-series analysis; Ives and his Australian co-authors now present further innovation. More specifically, they make use of the (extended) Kalman filter, a statistical technique for which its inventor, engineer Rudolf Kalman, received the US National Medal of Science in 2008. The filter smooths out the system's stochasticity and, in parallel, provides an estimate of the model's statistical likelihood.

Comment Source:This describes an example of state-of the-art ecological theory: [Theoretical ecology: Waltz of the weevil](http://www.nature.com/nature/journal/v470/n7332/full/470047a.html), Nature 470, 47–49 (03 February 2011) doi:10.1038/470047a You might like to mention it in week 309. I think it's an example of [[stochastic resonance]]. Certainly it uses a [[stochastic differential equation]] and other things that have been mentioned here. Quote: > Modern time-series analysis came to the rescue. Theoretical ecologists are familiar with the contributions of one of the authors (Ives) to ecological time-series analysis; Ives and his Australian co-authors now present further innovation. More specifically, they make use of the (extended) Kalman filter, a statistical technique for which its inventor, engineer Rudolf Kalman, received the US National Medal of Science in 2008. The filter smooths out the system's stochasticity and, in parallel, provides an estimate of the model's statistical likelihood.
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3.
edited February 2011

Cool! Kalman filters! I need to learn about those...

Curtis wrote:

We spent four solid days touring a small fraction of the different ancient temples. A week should be just about right.

Good — I thought we might get a bit bored, but the Lonely Planet says a week is good... and frankly I really enjoy getting "a bit bored" in a new place, instead of zipping in and out at a frenetic pace. It takes time for the atmosphere to soak in.

Comment Source:Cool! Kalman filters! I need to learn about those... Curtis wrote: > We spent four solid days touring a small fraction of the different ancient temples. A week should be just about right. Good &mdash; I thought we might get a bit bored, but the <i>Lonely Planet</i> says a week is good... and frankly I really enjoy getting "a bit bored" in a new place, instead of zipping in and out at a frenetic pace. It takes time for the atmosphere to soak in.
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4.

John wrote:

Cool! Kalman filters! I need to learn about those...

When you'll do that, you'll find that there is already a stub called Stochastic filter ready to expand...:-)

Comment Source:John wrote: <blockquote> <p> Cool! Kalman filters! I need to learn about those... </p> </blockquote> When you'll do that, you'll find that there is already a stub called [[Stochastic filter]] ready to expand...:-)
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5.

I think I mentioned on another thread that I'd tested out running it in Sage and I still have it public on sagenb.org. I'll put Graham Jones as creator as I saw I forgot that. Or do you want make it private again?

Comment Source:I think I mentioned on another thread that I'd tested out running it in [[Sage]] and I still have it public on sagenb.org. I'll put Graham Jones as creator as I saw I forgot that. Or do you want make it private again?
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Staffan wrote:

Or do you want make it private again?

I don't know who "you" is. I don't want it private, but I'm not sure I know what you're talking about — maybe you're talking to Graham?

Anyway: I put week309 onto the blog; that's all I was able to do this week, despite my grand dreams.

I will leave for Cambodia tomorrow, so it would be very nice if Graham or anyone who feels up to it tackles any questions that may come up regarding week309.

I didn't wind up talking about the "waltz of the weevil"... maybe I can remember to do that when I discuss stochastic resonance!

Comment Source:Staffan wrote: >Or do you want make it private again? I don't know who "you" is. I don't want it private, but I'm not sure I know what you're talking about &mdash; maybe you're talking to Graham? Anyway: I put [week309](http://johncarlosbaez.wordpress.com/2011/02/17/this-weeks-finds-week-309/) onto the blog; that's all I was able to do this week, despite my grand dreams. I will leave for Cambodia tomorrow, so it would be very nice if Graham or anyone who feels up to it tackles any questions that may come up regarding week309. I didn't wind up talking about the "waltz of the weevil"... maybe I can remember to do that when I discuss stochastic resonance!
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7.

Graham wrote:

This describes an example of state-of the-art ecological theory: Theoretical ecology: Waltz of the weevil, Nature 470, 47–49 (03 February 2011)

Comment Source:Graham wrote: <blockquote> <p> This describes an example of state-of the-art ecological theory: Theoretical ecology: Waltz of the weevil, Nature 470, 47–49 (03 February 2011) </p> </blockquote> I don't have access to Nature...
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8.

So how was Cambodia? What did you think?

Comment Source:So how was Cambodia? What did you think?
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9.
edited March 2011

It was fascinating! Great in some ways, very sad in others. I want to blog about it, but I've been too busy ever since I got back. So far I just have one photo on my website:

Lisa in the ruins of Ta Prohm.

Comment Source:It was fascinating! Great in some ways, very sad in others. I want to blog about it, but I've been too busy ever since I got back. So far I just have one photo on my website: <img src = "http://math.ucr.edu/home/baez/diary/cambodia/ta_prohm_lisa.jpg" alt = ""/> Lisa in the ruins of <a href = "http://en.wikipedia.org/wiki/Ta_Prohm">Ta Prohm</a>.