anarres

foooooo

Post from friendica to dreamwidth worked, does it go the other way?

Deutsche Welle, sort of a German equivalent of the BBC, provides short current-affairs-type programs written in simple German and read slowly, for German-learners to practice on. I've been working my way through these and my particular favourite is Gemeinsame Klug or "Together Wise", a charming story about a scientist who wants to find out how a swarm of fish are able to move as if they were a single individual. She builds a robot fish which swims among the real fish, and attempts to lead them away from food. When a group of only two fish are infiltrated by the robot, they do indeed follow it, but when Robo-fish infiltrates a larger swarm, the other fish refuse to follow its lead. The researcher concludes that the swarm will only follow if a certain minimum percentage of the fish take the lead.

I have no idea how true this story is but it really caught my imagination, and I found myself wondering exactly what determines whether the fish move as a swarm, and what advantage they gain from this.

Logo of Radical Routes network of housing co-ops


It's obvious that fish don't ALWAYS act as a swarm, otherwise there would never be any leader fish to lead the swarm in a new direction. So it must be that fish have both an autonomous-mode, where they make their own decisions, and swarm-mode, where they follow the group.

I'm pretty sure that if there was some kind of clear danger, say, a shark approaching, any given fish would autonomously swim away no matter what all the other fish (or robotic infiltrators) were doing. It seems to me the only situations where there would be an advantage to acting as a swarm would be those in which it wasn't entirely clear what the correct decision would be. For example, some of the fish in the swarm faintly detect a hint of danger, which might be an approaching predator, or might be something completely harmless (a passing submarine, say).

Let's say that one in twenty detect a faint whiff of danger. So 5% of the fish swim away, in autonomous mode. Since this is all the information we have about the situation, we can say that, there is a 5% chance of imminent shark attack.

Is it advantageous at this point for the fish to act as a swarm, all following the 'leaders' who are swimming away? There is a 95% chance that swimming away is the wrong decision, with no shark nearby (maybe the sound is really something harmless. It could be a bunch of marine biologists making a documentary, Jaques Cousteau-style. Making a correct decision has a benefit (not getting eaten by sharks) but making a wrong decision has a cost (wasting calories swimming away unnecessarily, and possibly swimming away from food and thus missing out on dinner). The benefit and cost are not equal: in this case the benefit (not getting eaten) weighs more heavily than the cost (wasting calories).

The minimum fraction F of fish swimming away which tips the rest into swarm behaviour should be determined by

FB + (1-F)C = 0,

where B is benefit and C is cost. So, when a fraction F of fish in autonomous mode swim away, then the benefit of escaping the shark, if it exists, weighted by the possibility F that there really is a hungry shark nearby, is equal to the cost of swimming away in the event that there is no shark, weighted by the possibility (1-F) that the shark is actually a distant submarine, a group of marine biologists and their film crew, or the figment of some over-anxious fishes' imaginations. The fraction F that optimizes the fishes' chances of survival has been determined by a very long series of experiments carried out by the process of natural selection, with the fraction being set randomly to different values by mutations, and those groups of fish having less-optimal values having a greater frequency of being eaten by sharks. Probably. I actually have no idea if that is right or not, since I'm neither a statistitian nor an ichthyologist.

I did a quick google images search for "Robot fish", and came up with this charming creature:
Actual robot fish. Apparently it is used to clean up pollution, somehow. It comes from this website: http://www.bmt.org/News/?/3/0/510.

Hmmm. It seems like it isn't possible on a Dreamhack to access a module in the ~/dw/cgi-bin/DW/Controller folder. This:

---------------------------------
#!/usr/bin/perl

use lib "$ENV{LJHOME}/cgi-bin";
use DW::Controller::Nav;
---------------------------------

produces this:

Name "Template::Filters::BASEARGS" used only once: possible typo at /usr/lib/perl5/Template/Base.pm line 49.
Name "Template::Context::BASEARGS" used only once: possible typo at /usr/lib/perl5/Template/Base.pm line 49.
Name "Template::BASEARGS" used only once: possible typo at /usr/lib/perl5/Template/Base.pm line 49.
Name "Template::Service::BASEARGS" used only once: possible typo at /usr/lib/perl5/Template/Base.pm line 49.
Name "Template::Provider::BASEARGS" used only once: possible typo at /usr/lib/perl5/Template/Base.pm line 49.
Name "Template::Plugins::BASEARGS" used only once: possible typo at /usr/lib/perl5/Template/Base.pm line 49.

and you get the same message if Nav is replaced with any other Controller module.

I could try to figure this out, or I could just work around it... I think I'm going to work around it :-)

Dear Anarres of the future,

If you ever find yourself thinking, 'I don't reaaaaally understand this problem I'm working on, but instead of methodically learning how to do it properly I'm just going to wing it, and if I can't immediately get it to work, well, I'll just randomly try to change a bunch of things until it does, and I'm sure that will end up saving time in the long run'... no. No, no, no, no, no, no, no. Wrong, no points. You fail.

You've been told.

Sincerely,
Anarres of the present.

Don't you hate it when your thoughts are all running together and you end up writing a blog entry about three different things instead of having separate posts?

I make electronic music as a hobby. Um... 'music' is almost too grandiose a word for what I do. I make electronic noises as a hobby. For a couple of years I had been generating sounds with AmSynth, and then one day I updated Ubuntu and, oops, AmSynth broke. So I spent some time in forums trying to find a way to fix it and, long story short, couldn't find a reasonably easy solution, and so gave up. I started using ZynSubAddFX, which I viewed as being OK, but not quite as good as AmSynth. So fast forward to a few days ago, I upgraded to the latest version of Ubuntu and, hey, AmSynth works again, yay!

Except, I played with it a bit and... I found that I actually prefer ZynSubAddFX now.

I've been having trouble getting the statistics pages /stats/site and /admin/stats to work on my Dreamhack, and after trouble-shooting it turned out that the Dreamhack server was simply too overloaded to deal with those pages, the solution was to get a shiny new Dreamhack on a different server, it works great, joy :-)

And I went on an epic quest to buy sandals today. Because it is around 30 degrees here most days and I am in the beautiful city of Berlin and I like walking around a lot, and the old sandals were not really comfortable for walking any distance. I wanted the kind that are basically like hiking shoes, but sandals. I went into 4 or 5 different shops (which was hard, shopping is my least favourite thing ever) and was thoroughly disgruntled by the fact that most of the comfortable, practical sandals are only available in men's sizes, while the women's section has rows and rows of useless flimsy things. Really, about 70% of the women's you can buy border on being torture devices, they do look very pretty but you wouldn't want to wear them. Maybe we should re-classify high heels as being ornaments rather than clothing? Then people would put the high heeled shoes on their coffee table as art and wear shoes that don't shorten their achilles tendons.

Anyway. I got some good sandals, the brand is Ecco and they are pretty comfy. They cost more than I have ever spent on sandals before but my feet tell me it was worth it.

Make a patch:

$ diff -u oldfile newfile >> file.patch

(> overwrites, >> appends). The -u means unified format. Apply patch to (some other version of) oldfile (yes it does have to have the same name, no you don't have to specify the name, it figures out on its own which file to apply the patch to, and yes it does overwrite the old version):

$ patch > file.patch

Creating a patch that creates a new file: to do this you have to compare directories, not files. Yikes! Before doing anything else get Dreamhack up to date, and then get rid of all the clutter.

To make a patch comparing directories:

diff -u -r -N ~/temp4 ~/temp5 > folder.patch

the -r makes it recursive, and the -N means new files can be created as part of the patch.

My mission for today is to learn about the Template Toolkit. I've tried to look at TT a couple of times already, each time, aw, yeah, this is going to be really easy, but I came out feeling completely mystified. So I've been putting it off, and thinking, maybe I can get away with just using BML, but since Dreamwidth as a whole wants to move from BML to TT it seems like it would be a bit perverse to do new work in BML. So, today is the day that I sit down, drink coffee, and figure it out.

I've posted this, so now I have to :-P

Gearman and Schwartz are both for running server scripts that will take more than a couple of seconds. Gearman does things at a precise time and Schwartz gets them done at some not-precisely-determined time. Workers use the Schwartz.

Check on how the Schwartz is doing by going to ~/dw/bin and doing this: $ perl schwartzmon --help

/admin/stats displays only if logged in as a user with 'payments' priviledges.

The stats system only works if bin/worker/stats-collection was run within the past 24 hours. This can either be done by a worker or run manually.

Both /admin/stats and /stats/site on dreamhack sometimes show only a blank page, but they sometimes work if you close all other tabs, or log out and then log in again.

I'm doing the exam study thing, which is frustrating - my courses are interesting but exam study makes you forget this and just focus on getting marks. I'm really excited about the statistics project, but I have to wait for exams to be done before I'll be able to spend a serious amount of time on it.

On my way into uni I take a slight detour so that I can walk along Castlefield canal basin instead of along a motorway. Not many people come by this way. I usually pass by this family of geese, two big ones and five little ones.



The big ones are really very big and actually quite intimidating - they've got big, scary, bitey beaks and they hiss at me to let me know they're pissed off that I've entered their space. The small ones are fuzzy and yellow and very cute, and totally oblivious to me. I sometimes stop for a few minutes to watch them (from a respectful distance) and as far as I can tell they have three activities: pecking the ground for food, grooming themselves, and grooming each-other. They have a funny way of walking around, going a few steps in one direction, pecking the ground, then switching to a different, random direction. Brownian motion - not a good strategy for traveling from A to B, but a very good searching strategy. Their path has a fractal dimension somewhere between one and two and in theory if they walked for an infinitely long time their path would completely fill a two-dimentional area.

My procrastinate-o-meter is pinging, better get back to work.