| The philosopher's axe redux |
[Jul. 2nd, 2009|08:04 am] |
All the way back in 2006, I wrote about the problem of the philosopher's axe: if you replace the shaft, and then later you replace the head, is it still the same axe? So as you can imagine, I was delighted to discover the existence of the Helko modular axe system.
In contrast to my ice-climbing friend, I was interested to note, they think that having to replace the axe's handle is more likely.
But according to the always-interesting Eliezer Yudkowsky, the whole notion of particles having a continuing identity in time makes no sense on a quantum-mechanical level, so the whole question is moot anyway. |
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| Are you ready to get pumped? |
[Jun. 26th, 2009|12:02 am] |
Hi, this post is about Factor, real Factor. This post is awesome. My name is ![[info]](http://l-stat.livejournal.com/img/userinfo.gif) pozorvlak and I can't stop thinking about Factor. Factor is cool, and by cool, I mean totally sweet.
Facts:
1. Slava Pestov is a mammal.
2. Slava Pestov hacks on Factor ALL the time.
3. The purpose of Slava Pestov is to flip out and kill people.
Weapons and Gear:
1. Concatenative (stack-based, Forth-like) language.
2. Dynamic types.
3. First-class functions.
4. Object-orientation.
5. Real macros.
6. Batteries included.
7. The listener: debugger/REPL/help browser/etc.
8. Optimizing, self-hosting native-code compiler.
9. Ninja stars.
Testimonial:
Factor programmers can kill anyone they want! Slava cuts off heads ALL the time and doesn't even think twice about it. The guys on #concatenative are so crazy and awesome that they flip out ALL the time. I heard that littledan was eating at a diner. And when some dude dropped a spoon littledan GC'ed every object in memory. My friend Mark said that he saw a Factor programmer totally uppercut some kid just because the kid opened a gl-window.
And that's what I call REAL Ultimate Power!!!!!!!!!!!!!!!!!!
If you don't believe that Factor programmers have REAL Ultimate Power you better git clone their repository right now or they will chop your head off!!! It's an easy choice, if you ask me.
Writing OpenGL code in Factor:
Step 1: Look for some Factor OpenGL documentation.
Step 2: Fail to find any.
Step 3: Get really super pissed.
Step 4: Get some C++ OpenGL documentation instead.
Step 5: Put something slippery on it, like butter or cream.
Step 6: Bend it to fit (this is crucial).
Step 7: Keep folded and insert into listener hard.
Step 8: Push hard until you can't see it.
Step 9: Wait.
Step 10: Die.
If you succeed, everybody will be like “Holy Crap!”
Update: by popular demand, a picture of Slava wailing on guitar. |
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| Response to a frustrated calculus student |
[Jun. 20th, 2009|01:08 pm] |
Over on math.reddit, someone was complaining that "Calc II is destroying [him/her]". I wrote a longish response, and thought I'd repost it here.OK: first, breathe. 47 days is ages.
You shouldn't have to memorise much at all for a basic calculus class. There's nothing in there that can't be derived in a couple of minutes if need be. Since rote memorisation doesn't appear to be your strong suit, I suggest you take this approach instead. When your instructor tells you to memorise formula X, learn how to derive it instead. Look through the proof, and identify the "key moves" that make it work - usually, a proof has just one or two of these, and then the rest is just mechanical manipulation. Learn what the formula's for - don't think of (say) integration by parts as Yet Another Damn Thing you have to learn, think of it as a handy technique for finding integrals of products, derived by applying the product rule for derivatives to u*(integral(v)), integrating both sides, and rearranging. Sounds like more memorisation, albeit of a slightly different form? Maybe, but it's a lot easier: integration by parts has to do with integrating products, and integration is the inverse process to differentiation, and so the product rule's a pretty obvious place to start. Write that down, and then follow your nose. If you're uncomfortable following your nose (or even if you're not), I recommend Polya's book How to Solve it.
This way, you'll both understand each individual result better, and better see how to fit them into the framework of the whole subject. And you won't be thrown by problems which aren't exactly like the ones you've come to expect: you'll understand which tools in your toolbox are applicable and which aren't.
Don't worry if this isn't the approach your instructor recommends: different people respond to different methods of teaching, and it sounds like his/her technique is a really poor fit for your brain.
Another thing is to be really careful with your basic algebra. Calculus can involve a lot of symbol-bashing, and a mistake early on can cost you a lot of time. Sanity-check your results whenever possible: does it make sense at zero or one, does it have the sign you'd expect, stuff like that.
Lots of people here have said that learning the meaning of "dx" is key to mastering the subject. To tell you the truth, I've taken something like ten years of calculus classes, from high school through to postgraduate level, and I'm still not entirely sure what it really means. If you get the chance, take some courses on differential geometry and exterior algebra some time, it's fun stuff. But at your level, it's certainly very helpful to think of it as meaning "a very small change in x". Another useful sanity-check/heuristic derivation is to draw little diagrams with small changes in the variables you care about and derive approximate expressions for the relevant change in the quantities you're trying to calculate. |
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| FAO: immune system |
[Jun. 19th, 2009|09:43 pm] |
We appreciate that this is a difficult time of year, that you're all on high alert and every pollen grain sets the alarm systems off, but the last thing the Firm needs is another cold, mere days after we got over the last one. And we need hardly remind you that that one took nearly a month to get over.
Do buck up, chaps. We know you're capable of better than this.
Sincerely,
The Mgt. |
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| i18n results |
[Jun. 17th, 2009|09:27 pm] |
Thanks to everyone who responded to my recent post about internationalising this blog. The respondents were unanimous in saying that they were perfectly capable of working out, Googling for or asking about any points of difficulty, and inline explanations would probably just break the flow. So I'll stop worrying about it: but if anything's unclear, please ask.
neoanjou also made the very good point that literal translations (especially of units) often aren't very helpful if you don't have the context needed to interpret them. Is £10 a lot for a meal in a restaurant? Depends where you are.
Serendipitiously, I just came across a nice example of the dangers of literal translation. The label that came with the North Face duffel bag I won in a raffle last year proudly declares "Bomber Construction". Which doesn't mean it's shaped like a Flying Fortress: in climbers' argot, "bomber" is short for "bombproof", hence really solid, totally reliable, etc. Unfortunately, nobody told the French translator, who rendered it as "Structure de type « aviateur »" :-) |
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| i18n |
[Jun. 14th, 2009|10:06 pm] |
One of the unexpectedly great things about this blog is the international character of its readership. While most of the people reading this are, like me, British, we've got Americans, Russians, Australians, Swedes, a Bangladeshi or two, and no doubt others I'm forgetting.
This complicates the process of writing, though, since it makes it more difficult to decide how much common ground I can assume between me and my readers, and how best to express myself. I'd appreciate your help on setting some sort of policy.
I think the only way this thing will continue to work is if I write about things that interest me, some of which will be of mainly local interest, so expect the occasional post about UK politics and so on. I'll try to provide explanatory links, as I did here - is that OK? Given that I'm a Brit, writing for an audience that's mostly other Brits, I make no apology for writing in British English; but the language of the Web is US English, and the differences are occasionally significant. Would it be helpful to provide occasional translations? Suppose I were to talk about an off-licence: would it be helpful or annoying to write "(liquor store)" afterwards? Actually, after four years in Scotland, I'd be more likely to say "off-sales" these days, which adds an additional layer of complexity. How about units? I tend to think in a godawful mess of Imperial and SI units, depending on what I'm measuring¹ and how big it is. Is it helpful to provide conversions, say "10st/140lb/63.5kg", or is that an insult to your ability to use Google Calculator? How about climbing grades (which are notoriously difficult to translate, because different grading systems take different things into account). Would it help anyone if I were to describe Cenotaph Corner as "E1 5c (approx F6a+², US 5.10b or a hard Aussie 18)" rather than simply E1 5c?
Opinions eagerly sought. Also, if you reading this from somewhere exotic, please say hi!
¹ A Canadian friend tells me that Canadians use metric units for everything except personal measurements: height, weight and penis size.
² I'm wondering if I've done that conversion right: it looks far harder than that from the bottom... I guess climbing indoors (where my experience of French grades comes from) is a fundamentally different experience from trad climbing outdoors. |
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| One my Russian readers will probably already know about |
[Jun. 14th, 2009|09:42 pm] |
Ten probes from the Venera series successfully landed on Venus and transmitted data from the surface, including the two, Vega program and Venera-Halley probes. In addition, thirteen Venera probes successfully transmitted data from the atmosphere of Venus.
Among the other results, probes of the series became the first man-made devices to enter the atmosphere of another planet (Venera 4 on October 18, 1967), to make a soft landing on another planet (Venera 7 on December 15, 1970), to return images from the planetary surface (Venera 9 on June 8, 1975), and to perform high-resolution radar mapping studies of Venus (Venera 15 on June 2, 1983). So, the entire series could be considered as highly successful. Totally. Fucking. Awesome.
There was a British space programme, briefly. I've heard it said that it could have got to the Moon for a tenth of what NASA spent, with their throw-money-at-problems approach, but that it couldn't have done it for 1/200th of what NASA spent, which was its actual budget. Sic transit gloria Britannorum.
There is also an Indian space programme, of which I expect great things in coming decades. |
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| (no subject) |
[Jun. 6th, 2009|10:33 pm] |
I've got a problem: I've had an idea I want to write about, but it depends on two or three other ideas I wanted to write about but never got around to. So I'm going to write this post in a top-down, Wirthian fashion, stubbing out those other posts: maybe, if there's enough interest, I'll come back and write them properly and replace the stubs here with links. OK with everyone?
Right, on with the motley.
Stub post no. 1
Extreme Programming (XP), whether intentionally or unintentionally (and my money is on "intentionally, but try getting them to admit it") is really good for getting work out of people who are bright but have short attention spans. This is a Good Thing. It's most obvious in the case of pair programming - imagine saying to your partner "Y'know, this is kinda hard. Let's surf Reddit for a while" - but actually, most XP practices have this benefit. Short feedback cycles, concrete rewards, definite "next moves" (given by failing tests and the "simplest thing that could possibly work" approach) - all of these things have the effect of maintaining flow and reducing the incentive to slack off. It's programming as a highly addictive game. Dynamic languages work well with this approach, because they make it as easy as possible to get something up and running, and to test the things you've written.
Stub post no. 2
Haskell is the opposite. It encourages deep thinking, and everything about the language makes it as hard as possible to get something running unless it's just right. Screw up, and you're not presented with a running program and a failing test that you can run in the debugger; you're presented with an unfriendly compiler message and a bunch of dead code that you can't interrogate in any meaningful way. After a morning hour few minutes of this (usually involving no small loss of hair), the consultant Barbie that lives in my head invariably says "Statically-typed pure functional programming is hard. Let's go shopping!" And I, fed up and mindful of my scalp, agree. This is why I am no good at Haskell.
Stub post no. 3
Everything I read by or about the climber Dave MacLeod (blog) makes me more inspired by him. Partly for his visionary climbs, but mostly for his approach to choosing, training for and tackling really hard problems, which I think should generalise really well, if only I could put my finger on what exactly it is. It helps that he's a really friendly, pleasant guy in person. Check out the BAFTA-winning film Echo Wall that he and his wife made about his preparation for his first ascent of the trad route of the same name. If you're in Edinburgh, you can borrow my DVD, I'm positively eager to lend it out.
Anyway, something Dave wrote about training (which I can't be arsed to find right now) said that in order to train effectively, you have to be constantly pushing yourself in some way: either in terms of power, or stamina, or technique, or fear¹, or whatever. You have to find your comfort zone and then consciously go beyond it, in whichever direction you wish to improve. As you improve, your comfort zone shifts, and you need to keep pushing yourself harder and harder in order to continue to improve. But (and here's the interesting bit), he said that if you do this for long enough, your whole conception of comfort shifts, and you start to feel uncomfortable if you aren't pushing yourself in some way.
So, here's the thought I had. Maybe all the Haskellers have been training themselves Dave MacLeod-stylee, and now only feel comfortable pushing themselves really hard, and that's why they like using such a bloody difficult language.
¹ About a year and a half ago, I was seconding a route called Dives/Better Things (Hard Severe) in Wales, and got to a bit that was a bit too hard and a bit too scary. I floundered around for a bit, getting more and more freaked out, and then said to myself "What would Cale Gibbard do? He'd pause for a bit, think really hard, work out exactly what to do next, and then do that. OK. Do that, then." I have no idea if Cale climbs, but it did the trick. Cale, if you're reading, thanks for that :-) |
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| Wedding |
[Jun. 2nd, 2009|09:02 am] |
We went to elvum and terpsichore1980's wedding at the weekend. Which was lovely: both in the sense that it was great to see two such well-matched people get married, and to see two good friends be so happy; and also in the sense that the actual day itself was brilliant. I tried to say this to terpsichore1980 towards the end of the reception, but (excellent) drink had tied my tongue, and what came out was "Every single thing about this wedding has been a little bit better than it needed to be." Which could so easily have been misunderstood. Fortunately she's both lovely and perceptive and understood what I meant, but I still want to take this opportunity to clarify myself. So. Even though I knew how long they'd been planning the wedding, and had some idea of how much work had gone into it, nonetheless my high expectations were consistently exceeded. It was clear that they'd thought hard about every single detail, and found a way to make everything excel. Truly a day to remember. I can only think of one wedding I've enjoyed half so much. Congratulations to all those involved!
All the best to the happy couple for their life together, and I look forward to hearing the reports of their honeymoon in California :-) |
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| Another daft idea |
[May. 26th, 2009|07:42 pm] |
Sleeping bags with sleeves, allowing for the following use cases:- Cuddling in tents. Because I'm soppy like that.
- Sitting around in, say, a fscking cold flat in winter.
- Camping in cold situations, where you want to do your sleeping bag all the way up but don't want to risk being unable to unzip yourself later.
The sleeves should terminate in mittens, for Safety. To support use case 2, the mittens should perhaps be the type where the end can be folded back to reveal the wearer's fingers.
There's prior art: several brands of blankets-with-sleeves are commercially available. |
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| The Long 21st Century |
[May. 21st, 2009|11:22 pm] |
Historians sometimes talk about the "long 19th century", which covers the period from the French Revolution to the start of the First World War - the idea being that (in the West, at least) international relations, warfare, social structures and technology in the periods 1789-1799 and 1900-1914 were more typical of the 19th century than of the 18th or 20th. Eric Hobsbawm, who proposed this idea, then went on to propose the "short 20th century" as a natural historical period: in his view, the short 20th century should run from the First World War to the fall of the Soviet Union. Which means, presumably, that we've been living in the long 21st century since 1991. This commenter suggested that the rise of the Internet also makes a good starting point for the long 21st century (though the September that never ended began in 1993).
[It's worth pointing out that redefining the endpoints of your period to include any grey areas is a standard move in the power games played by different schools of historians - Renaissance historians typically put the start of the Renaissance a couple of hundred years earlier than medievalists, for instance. Hobsbawm was just more blatant about it than most. Googling for "long nth century" turns up some relevant hits for most n between 1 and 20, often, entertainingly enough, for two consecutive values of n.]
Anyway, I agree with Hobsbawm and Dresner, but for more pessimistic reasons: 1991 was also the year of the first Gulf War, and I think in years to come that will be recognised as the opening salvo of the Oil Wars of the long 21st century.
I was surprised to see that there are currently exactly 1991 messages in my Livejournal inbox. Coincidence? I think not. |
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| Threads |
[May. 15th, 2009|11:24 pm] |
My trousers, as is their wont, have all decided to fall apart at the same time again, so I've been doing a bit of sewing this week. I'm not much good at sewing, but I offer up what little I know about the subject in the hope that others may find it useful. Most of this was taught me by stronglight, mi_guida, half_of_monty and susannahf, some of it I remember from school, some was taught me by my mother, and some of it I worked out for myself. It's enough for basic repairs - mending holes and burst seams, that kind of thing. To make clothes from scratch or to carry out more advanced adjustments, you'll need to find a more knowledgeable instructor.
( Read more... )
Sewing's time-consuming, but it's also very satisfying, like most repair work. |
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| Nothing says "unprofessional job" like wrinkes in duct tape |
[May. 6th, 2009|04:41 pm] |
[mrpjantarctica is entirely to blame for this idea. My contribution was to recognise that the world market for it might be more than five. It's all about the marketing.]
Is there someone in your life whose boundless enthusiasm for fixing everything around them is matched only by their limited repertoire of skills and tools? The kind of person whose house is held together by string and cable ties, who believes there's nothing on God's earth that duct tape can't fix?
Stuck for something to buy them for Christmas?
Then get them the Bodger's Home Companion!
Contents:- One large roll of gaffer tape. Obviously.
- A can of WD-40.
- A job lot of rubber bands, cable ties and Jubilee clips, in a variety of sizes.
- A not-terribly-good multitool. I'm thinking one of these.
- A ball of string.
- A tube of epoxy resin.
- A short book, "101 Great [insert nationality here]¹ Bodges", containing instructions for a wide variety of half-arsed home and automotive repairs.
The de luxe version would also contain self-amalgamating tape and heatshrink sleeving, and possibly a soldering iron.
What have I forgotten?
A great advantage of the BHC over other novelty Christmas gift items is that it really doesn't matter if you get given three of them, there being no such thing as too much gaffer tape.
¹ Possibly some slight adjustments would be needed for different markets, but I reckon you could get a long way just by changing the title. I'm thinking of something more useful and less stupid than the output of the Duct Tape Guys. We would, of course, need a fearsomely comprehensive disclaimer of liability. |
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| Redefining the impossible |
[Apr. 30th, 2009|11:44 am] |
In the comments on my last post, I mentioned that My favourite example of spectacular theorem failure is flight: in a perfectly inviscid fluid, it's impossible (no viscosity means no starting vortex which means no circulation around the wing), but it is possible in a fluid with viscosity > 0, no matter how small. It's a rather beautiful result, I think, and should serve as a handy warning against people who want to convince you of something using their mathematical model whose assumptions are almost true. But (in the form stated above) it's not entirely correct.
The first thing to note is that I meant to say "heavier-than-air flight". As far as my dim recollection of fluid dynamics can tell me, there's no obstacle to flying a hot air balloon or an airship in a perfectly inviscid medium. However, propellors and fans are essentially sets of wings joined at the hip, so you might have some trouble propelling your craft anywhere other than where the wind was blowing¹. Which leads us to what I really want to talk about...
It turns out that there is a small wasp, Encarsia formosa, which makes use of an entirely different method of flight that does not require a starting vortex. It takes advantage of a hidden assumption of the impossibility proof: that the topology of the surrounding medium does not change. E. formosa, when in hovering flight, briefly touches its wingtips together at the apex: this changes the topology of the surrounding air, and gets around the prohibition. And indeed (see the papers referenced in that hastily-edited Wikipedia article) this method of flight would, apparently, work in a fully inviscid medium.
This sort of thing is surprisingly common, I find. Quite a few times over the last few months, I have encountered some problem that seems impossible to solve; typically of the form "I want to do both X and Y simultaneously, but X precludes Y because...". Several times I've gone as far as constructing a semi-formal impossibility proof, and a couple of times I've presented said proof to my boss as an explanation for my lack of success. And then, a few hours or days later, I've realised that while it may indeed be impossible to do what I've been trying to do, it is possible to achieve the desired effect in some other way: my impossibility proof contained some hidden assumption about the form of the solution, and by subverting that assumption we can proceed to solve the true, more general, problem.
So I think the lesson here (which seems almost comically trite, now I come to write it down explicitly), is that even if what you're trying to do is definitely, provably, mathematically impossible, you shouldn't necessarily give up straight away. Rather, you should attempt to redefine your notion of success, and see if you can achieve that instead.
¹ I suppose you could power your craft with a ramjet, but that leads to a chicken/egg problem. Engineers: am I right in thinking that conventional jet engines rely on a fan-like compressor to get started, and thus wouldn't work in a fully inviscid fluid? |
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| (no subject) |
[Apr. 29th, 2009|04:06 pm] |
There's a discussion going on over on ![[info]](http://l-stat.livejournal.com/img/syndicated.gif) simon_cozens' blog about the Fairtrade movement, and whether or not it does any good. A lot of the arguments advanced against it seem to boil down to "assuming no coercion, and fundamentally unrealistic conditions, Standard Economic Theory says it ought not to work", a line of argument that always makes me suspicious.
But anyway, this is an empirical question: do the problems that Simon and others describe occur in practice? Are the theorised benefits of Fairtrade realised in practice?
These are not easy questions to answer. So, I'm being lazy and asking here: is anyone familiar with the literature on this? |
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| Heffalumps! And coheffalumps! |
[Apr. 28th, 2009|11:14 am] |
Most people know the story of the three blind men and the elephant. There were three wise blind men (the story goes) who had never before encountered an elephant. One day, an elephant was brought before them, and they were asked to describe it. The first wise man felt the trunk, and said "Elephants are like snakes", the second felt a leg, and said "Elephants are like tree-trunks", and the third felt an ear and said "Elephants are like bats".
This story gave rise to the title of the mathematician Peter Johnstone's epic work Sketches of an Elephant: A Topos Theory Compendium. Topoi, you see, can be described from several different viewpoints, and it's not at all obvious that the different descriptions all describe the same object.
As is so often the case, the story of the blind men and the elephant has a dual version, which is less well-known but (IMHO) equally interesting. It concerns three wise, blind elephants, who had never before encountered a human being. One day, a human was brought before them, and they were asked to describe it. The first elephant stepped forward, and felt the human with its front hooves for a while.
"Humans," the elephant pronounced, "are flat".
And both the other elephants agreed.
I once told the dual story to Peter Johnstone. He didn't appear to enjoy it. |
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| (no subject) |
[Apr. 16th, 2009|11:51 am] |
A while back, I promised mrkgnao and necaris that I'd contribute something to the cultural/gaming webzine FerretBrain. I've been reading a lot of books about climbing and mountaineering recently, and I thought it might be interesting to do a sort of comparative review, interspersed with my observations on the general conventions of the genre (provided I can think of something more interesting than "a lot of mountaineering books are about times when it All Went Badly Wrong").
Anyway, here's a list of said books, compiled as much to aid my own memory as anything else. Any of them sound particularly interesting? Anyone like to recommend any other good ones I should read?
( The books ) |
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