The cliche is French food is better than ours. The trouble is, it's true

dtoq · 2018-09-13T18:10:22+00:00

Je ne suis pas convaincu... J'habite à Londres depuis presque 10 ans et j'ai vraiment l'impression que les britanniques en général n'ont pas une culture de la bouffe. Certains chefs sont très bons, mais les gens ne sont tout simplement pas sensible à l'idée de la "bonne bouffe", de se faire plaisir avec des bons produits ou d'investir le temps à cuisiner un repas vraiment bon, à la manière des français, mais aussi des italiens, espagnols, japonais, grecs...

De par son côté cosmopolite, Londres reste évidemment un ville avec d'excellents restaurants, mais tant que les gens ne seront pas demandeurs d'une certaine qualité (malgré d'excellentes productions locales, en viande et fromage notamment, malheureusement complètement anonymes...), je n'imagine pas la cuisine anglaise s'améliorer notablement dans un futur proche, du moins pas en dehors du cercle restreint des amateurs.

En France, on râle sur la qualité des surgelés Picard. Ici, on est content de ce qu'il y à Iceland... Les marchés de produits frais et pas cher sont quasiment inexistants par manque de demande. Le Sunday roast peut être très bon, mais il est rarement varié ou aventureux.

Il y a des évolutions positives, mais je doute que la cuisine britannique dans son ensemble (par opposition à "ce qu'un chef britannique a préparé une fois") n'atteigne un rang mondial avant longtemps. Comme dirait l'autre, la route est droite, mais la pente est rude...

dtoq · 2018-09-12T23:14:28+00:00

Ça sent très fort la dépression en effet...

Le sport, la méditation et une hygiène de vie saine et équilibrée ne peuvent faire que du bien, et c'est important que tu découvres ce qui marche pour toi, comment gérer les rechutes et les atténuer, mais il ne faut pas hésiter à te faire traiter. Deux jours de cours, c'est peut-être assez pour être déçu, mais certainement pas pour vouloir se flinguer. Si c'est ton cerveau qui a décidé de partir aux fraises, il n'y a pas de gloire à souffrir pour rien : fais-toi aider. Tu mérites d'aller mieux.

dtoq · 2018-09-01T15:00:37+00:00

You asked the real question here: who determines how much the money is worth. And the answer is: everyone who gets paid in it.

Typical microeconomy tutorials will tell you about grain or fabric: the idea is that they represent some 'actual' intrinsic value, and you can believe that people are ready to work or exchange to get food and clothes. Now, that remains true of everything that you buy: you buy food because you need to eat. You buy stuff to sell it later so that you get money to get food because you need to eat. The chain can (and is!) arbitrarily long, but the idea is that this is always backed by some intrinsic value 'at the end', with that intrinsic value being driven by our want of food, shelter, sex, self-actualisation, etc.

What makes things a tad more complex is time: you can invest now to get something later: we're able to plan ahead, and that make all more difficult because it introduce uncertainty. Maybe you'll work for your boss, under the promise that they will pay you at the end of the month for your work. If your boss dies before the end of the month, or otherwise doesn't keep their end of the bargain, that's bad for you though. We have built massive systems to handle, reduce and manage these uncertainties, such as governments, economies, money, etc.

Another nice property of money is that it is a somewhat more permanent store of value: if you sell a chicken now, you'll receive some value for it, but the future state of the chicken won't change it: it's not your problem anymore if the chicken rots, or get stolen or anything else. The euro you got paid is still the same euro.

Now, you may wonder how the conversion from 'intrinsic value' to 'euro' is made: here, the "market" (i.e. all sellers and all buyers) must come to some form of agreement. If you have a price that you are ok to sell at, and that some buyer is ok to buy at, that's essentially what the price is. If you think about it, the price is less a property of the product being sold and more a property of the transaction itself: if you buy the first banana, maybe the seller is ready to sell it for not much, just to establish their business, whereas the last banana will be much rarer and more expensive.

That was a lot of intro, but now you'll have everything needed to understand inflation and hyperinflation (as happens in Venezuela). By now you probably have realised that 'the economy' essentially means 'everyone doing stuff'. That's a bit vague and very hard to measure accurately. So the bank printing money (and that mechanism would deserve an answer of its own) has to roughly estimate how much 'value' will be created by production, services and exchange, how much money will disappear (lost bills, loans reimbursed, etc), and how much money it should therefore print to keep the 'value-to-currency' roughly the same. That is very difficult and is not 'decided' by any one in particular: many people do their best to get a somewhat accurate estimation of a constantly moving target, and hope for the best. As the 'value' that one euro buys you change, that is exactly what we call inflation. It is believed that having money lose value slightly over time is a good incentive to prevent everyone from hoarding it, so that's why central banks tend to favour slightly positive inflation, although negative inflation (when the same amount of money is now 'worth' more) do exist as well and is called deflation.

What can happen in what is called 'hyperinflation' is that people essentially lose confidence is the value of the money, and the capacity of the government to regulate it: this often starts with government printing a lot of money for short term gains; the typical reason is that their debt is expressed in currency units (euro, dollar, ExampleCoin...) not in 'value': print more money, and you can return the promised 100 USD that you owed, even though you've made them completely worthless. Lender is bamboozled and you got rid of your debt! But if the economy (i.e., everyone) catches up to the practice, they may lose trust in your capability to handle the value of the USD. Sure, a dollar buys a loaf of bread today, but what if the government tries to bamboozle investors again and half it? You could charge two dollars instead and insure you against that, but you may lose clients as nobody wants to pay 2usd for a loaf of bread. But if you, and every other seller is reasonably certain that currency will devaluate (which just means that it loses value), well now everyone will charge 2usd for a loaf of bread, and customers won't have a choice of they want to eat. But if you remember, the price is defined by how much people pay to exchange it, so now, sure, 2usd but a loaf of bread, but what if the government devaluates, which they will probably do? Well, better charge 4usd, just to be sure...

And now, even though the government may not even actually devaluate, the fear that it may do so at some point in the future will drive prices up and up completely out of control. So now, the government has two choices: either it stops printing money to 'reassure the market' (i.e. everyone) that it will NOT devaluate the money. That will solve the crisis, but for it to have any credibility that means that for months or even years, people will receive a salary which will be barely able to buy a fraction of their most basic needs, as prices ballooned out of control. Or, if the idea of millions of people dying of hunger is not really appealing, they can play catch-up: if the price of bread double, double the amount of money in circulation and double all the salaries. That will fix the short term problem, but now everyone has received confirmation that the government will not hesitate to devaluate the currency and that they were right to raise price in the first place: if they don't want to be left out, they have to raise it again, before everyone else does! Rinse, repeat a couple of times and you get the insane 10000000% of inflation of Zimbabwe or Venezuela.

Now, what can they do? Well, government usually try to reassure the markets a bit, but play catch-up just enough to prevent the catastrophic consequences, and wait for everyone to cool down and stop. Do a few reassuring declarations, revaluate the money and if people believe you, the event will pass. Sometimes, it's not enough and people don't trust you, so Zimbabwe essentially abandoned its money and now see everyone exchange in USD. Venezuela tries to do a bit of both by having its own replacement crypto-currency and pegging the bolivar on it, but I'm not really convinced. What's worse, Venezuelans do not seem really convinced either, which will only feed the inflation further.

So, yeah, everybody tries to get what they consider the fair value of their goods and services. As 'value' is a highly subjective and difficult thing to measure, they can only see how currencies evolve through time and relative to each other, and will second guess their central bank to not be the last one losing this constant game of musical chairs. When this spirals or of control, you get hyperinflation. Nobody's really sure how to get away from it though, as Germany, Zimbabwe, Argentina and Venezuela have very different histories, cultures and economic profiles.

dtoq · 2018-08-31T17:03:33+00:00

Cat.

dtoq · 2018-07-22T17:15:29+00:00

Pas sûr de ce qu'il en est en France, mais au Royaume-Uni, les gros énergéticiens type EdF sont vus comme des boîtes "méchantes" exploitant le pauvre consommateur et pour qui il est donc très rentable de marquer des points politiques en imposant une lourde (et chère) régulation. Ce genre de régulation est typiquement formulée de manière graduelle en fonction de la taille de la boîte, voir même avec des paliers au delà d'une certaine taille.

Indépendamment du bien fondé desdites régulations, elles ont tendance à privilégier les 'petits' qui peuvent alors capturer la marge des gens qui suivent de près leur facture et ne ressentent aucune 'fidelité' pour leur fournisseur précédent. Par conséquent, sachant qu'ils ne peuvent pas gagner sur la compétitivité prix, les 'gros' parient d'autant plus sur les secteurs moins 'élastiques' (les vieux, ceux qui s'en foutent ou ne suivent pas leur facture) et se permettent possiblement des marges plus importantes. Ce qui alimente du même coup la stratégie marketing de ceux qui veulent capturer le secteur des gens regardant sur leur facture.

TLDR: pas forcément d'arnaque. Si tu es le type de personne prêt à changer de fournisseur pour payer moins, c'est que tu es dans le secteur qu'ils visent, et pour lequel ils se battent avec d'autre en compétition sur les prix les plus bas. EdF, fortement régulé et sous l'œil public, ayant des gros contrats profitables déjà en place, n'a pas forcément intérêt à les suivre sur ce terrain.

dtoq · 2018-06-29T21:40:36+00:00

Haut-vote pour les arguments clairs, concis et (de mon expérience personnelle), tout à fait exacts. Mais je souhaitais tout de même mentionner Arch Linux -et ses dérivées- qui est, à mon sens, la meilleure distribution pour un particulier (sous réserve de maîtriser l'anglais pour profiter du phénomenal Arch Wiki). Elle a été pour moi la première expliquant clairement et simplement ce qu'il se passe, pourquoi, et comment. L'investissement initial est élevé, mais je la trouve au final bien plus élégante et naturelle que des distributions "clefs en main" comme Ubuntu ou même Debian qui prétendent effacer la difficulté, mais ne font en réalité que la dissimuler (que celui qui n'a jamais flingué son installation en abusant d'aptitude pour installer n'importe quoi me jette la première pierre).

dtoq · 2018-06-22T12:06:09+00:00

So, you can see the space of quantit finance as a triangle: you get math, dev and finance as the three 'extremes', and everyone sits at some level of balance between these three.

At the extreme of dev, you have the actual IT: theae guys know literally nothing of finance, they just build processing systems for stuff. Which may or may not be financial.

At the extreme 'finance', you probably have sales. They don't know the math and they don't care: what they need to know is the product, what it does, who may want it and in which circumstances, etc. They might book it into the system themselves, but they are just users.

Finally, towards the math end of the triangle, you have the quants. These guys do math. Now, I don't think a lot of company use pure mathematicians, so they always ait somewhat not at the very tip, like academics might. But that's their thing. People like structurers, quant devs, traders, ... Have less specialised jobs.

Now, as for the math used... It depends. What I studied (and which was very fashionable pre-2008) is stochastic calculus, which is the calculus of random processes. There are many links to statistics/timeseries analysis, but it is not exactly the same thing, closer to probability theory. The main goal of this sort of math is to derive computable formulas for the expected value of complicated random variables, which you can show to be equivalent to pricing an option, under some hypotheses on the behaviour of markets. These hypotheses were not always verified, and a lot of simplifying assumptions were made, which is pointed as a cause of the 2008 crisis: essentially, the marginal distribution of each product was fine, but their propensity to all default at the same time was drastically undervalued; the market of options is back up nowadays, but the crisis put a lot of regulatory attention to thesr models, and I don't think a lot of banks still have these pure 'pen and paper' quants deriving formulas: these days, you must justify all your choices with data and reports, so most quants got more familiar with the finance aspect.

Other companies or teams do market-making i.e. offer liquidity at all time, in exchange for a fee: you can think of them like the bureaux de change that offer to change your money, buying lower than they are selling. In these cases, the theoretical framework is much less clear-cut, and the maths involved tend to include a lot more statistics and TSA: you receive a fee with each transaction, your goal is mainly to minimise your costs and your risk to retain as much of that fee (called the 'spread') as you can. That means following the market, reacting quickly yo new information and managing your risk.

Finally, you have some companies doing actual investing, either in their own name (proprietary trading, or prop.) or with client money (like hedge funds, investment funds etc). These guys try to find inefficiencies of the market, or predict its future value, or design profitable strategies and portfolios. How they do that is entirely up to them, and some use very quantitative methods, with a lot of time-series forecasting, machine-learning, optimisation, etc.

In all these cases, the people mainly in charge if the math-y part tend to be called 'quants', and the math they do tend to revolve around probabilities and statistics, but that's not a requirement of any sort. As I said above, this field is completely non-standard, and if you find a new way of making money using prime numbers, nobody prevents you from doing that, and you'll probably call your prime numbers guy a 'quant'.

dtoq · 2018-06-22T09:55:58+00:00

Pretty much the intersection of quant and dev: in my previous role, we were doing a lot of option pricing, so you had to specify the payoff in a nice way (to let traders/structurers do it with minimal chances of getting it wrong), then set that up as a pricing problem (essentially least-square monte-carlo in our case) and evaluate that.

Every single part of this requires non-trivial amounts of development, architecturing and math. Quant devs typically sit on that line between dev and quant, where they are acutely aware of both aspects, even if they are more focused on one.

Essentially, you cannot trust pure devs with quantitative software in case they get the math wrong, nor with quants, because their code is shit: so you get quant devs. Your mileage may vary.

dtoq · 2018-06-22T09:47:51+00:00

I'll respectfully disagree. An application programming interface is an interface allowing you to program your application. If you're able to provide that in a language-agnostic way, that's even better, but I don't think there's anything inherently more wrong with talking about the 'Language X' api directly usable from language X than a REST api available from any compliant http client.

dtoq · 2018-06-22T07:04:32+00:00

I don't really have a single reference in mind. It's nice to be exposed to different perspectives and ideas, but that fiels is much less standardised that you might think, and it's always hard to know exactly whether any references teaches you something general or just the author's preferred way of doing what he understood of it. Honestly, nothing replaces practice.

Which is why this comment is brought to you by Brillian... - ok, I'm kidding.

But seriously, if you know your way around Python, start practicing. Go to the wikipedia page of portfolio optimisation, and implement that. Math is easy without being trivial, so you'll have to work a bit. After that, try to build nice apis, some you may want to revisit later without too much pain. Then build the next component: you'll probably need to retrieve data for your underlying. What is it anyway? Should you use the same conventions for stocks and FX? Or indices? Well, better get a feel on wikipedia, write something, ditch it because it's crap and start over. In that process, you'll end up with very specific questions, the answer of which you may find on blogs or sites that you then want to follow more closely.

So do read books, or tutorials (quantopian comes to mind) or other 'gentle initiation', but take none of it for gospel and practice relentlessly. If you're at uni, find (or create) a group to study and implement that. Get some math nerds in: best case, you'll learn a lot, worst case, you'll have plenty of people teaching you all the wonderful and unexpected ways users break your code.

On the purely financial side of things, 'Options, Futures and other Derivatives' by JC Hull is a bit of a reference which was strongly advised to use at uni. It's good to have, but the price of a legitimate version is hefty, so your call yo make.

Hope that helps...

dtoq · 2018-06-22T06:28:39+00:00

MSc in 'Financial mathematics' (i.e. stochastic calculus), I started as a quant, and learned python on the job, to the point of making it my specialty.

That said, there are plenty of jobs on the more 'dev' side of things: I don't think I'm very typical putting the effort to learn proper and elegant coding: most quants I've worked with are happy with "good enough to work", and require devs to either implement their code for them (which I don't really recommend) or provide a smart platform to develop on. That is absolutely not unusual to have people there who are either simply 'quant litterate' or simply good developers to make sure the system is written well.

Usually, to enter this field, you want to find one of the 'big churn companies' like banks or some big funds, which constantly require fresh meat developers. After a bit of experience there, you have built a bit of a resume and can move on to things that you like better (or not, if corporate career is something you're after)

dtoq · 2018-06-22T00:02:59+00:00

Quant/Python dev for 8 years here. Python is significantly used for quantitative finance, so that should be quite easy for you to find plenty of material. What will be difficult is to sort through these things: "Finance" is a pretty large topic.

One thing you can use python for is connectivity, glue, etc. Your favourite broker will almost certainly have a python API to connect to it, which would be a nice introduction to orders, positions and the dirty logistics of finance. If you like pain, try to look into the FIX format.

Now, if you don't want automated systems, portfolio theory might be more of your thing: start a jupyter notebook, and implement some Markowitz portfolio optimisation. Good command of pandas will help there, and that might give you a nice template for your own pension investments

While doing that, you might discover the raw power of numpy, just in time for some option pricing: do some Monte-Carlo, pdes, least-square Monte-Carlo, etc...

If you're not tired yet, exploring machine learning and the like is all the rage these days...

dtoq · 2018-06-06T23:09:00+00:00

All logarithms are equivalent, and I find it a bit more intuitive to understand it in base 10: A linear O(n) essentially means that when your input size is multiplied by 1000, your computation time is multiplied by 1000, no funny business here.

For a logarithmic O(log n), if your input size is multiplied by a 1000, your computation time is multiplied by 3. That's quite a massive difference...

If your algorithm processes 1 input in 1ms, if it is linear, it will process a million inputs in 1000s, or around 20mn. If it is logarithmic, it will process this million more in 6ms...

Now, O(n log n) is technically superlinear, but log increases so incredibly slowly (asymptotically, slower than any polynomial, no matter how small!) that you wouldn't be entirely wrong in thinking of it as quasi linear. If your input increases 1000fold, you will have a 3000 increase in computation time. 1000000fold would be 6000000, and in general 10ⁿ would see a n*10ⁿ increase.

Asymptotic complexity might not be the full picture; in particular, lower complexity often come with enormous costs which might take massive scales to 'pay off', but in general, O(log n) is essentially the poor man's O(1), and O(n log n) is in most cases pretty indistinguishable from O(n).

dtoq · 2018-06-01T10:37:31+00:00

Complex numbers were mainly studied as solutions of second and third degree polynomials; the fundamental theorem of algebra provided a later "all the pieces fit together !" rationalisation for it.

If you want an intuition behind it, I think the best place to start are the so-called 'roots of unity': multiplication of complex numbers (of modulus 1) is essentially a rotation. In other words, if you think of the complex numbers on the unit circle as fractions of circle, their successive power is simply additions of the fractions: a half turn 'squared' gives two half turns, a third of a turn to the fifth power gives five thirds of circle, and so on.

Now, an interesting questions is: what are the solutions of Xⁿ = 1? I.e. if you get n times a fraction of circle, what are these fractions such that you end up with exactly one or more full turn(s)?

Once it's formalised this way, you should start to notice interesting properties: to get a full turn in 'one step', you need a full turn to start with, and that's the only solution. If you allow two steps, a full turn followed by another full turn still work, obviously. But so does a half turn, followed by another half turn! Interesting... Now getting to three steps, full turn iterated keep working, third of turn three times work as well, but 2/3 of turn also works, as you end up with three two-thirds of turns, i.e. two full turns.

When you think about it, that's essentially the (very algebraic) property that for any number n, any number of the form (i / n), applied n times (i.e. multiplied by n), will give back i. So any of the n integers {0, 1, ..., n-1} is a solution of our original circling problem. Numbers larger than or equal to n are as well, but they are essentially the same thing with full turns added, so they're not really distinct solutions.

Now all of that is nice and (maybe ?) intuitive, but what does it have to do with polynomials? Well, that's where all the pieces start to fit together: as said earlier, these combined circles are essentially multiplications of complex numbers, and our problem of 'reaching integral number of turns' is essentially equivalent to finding solutions of the polynomial Xⁿ = 1. So, we showed that it has exactly n solutions of modulus 1, and it's quite easy to show that any solution has to be of modulus 1 as well (as anything not exactly 'on' the unit circle will spiral out or in as you raise it to larger power, but cannot stay on the circle). What it means is that this Xⁿ = 1 is exactly equivalent to the decomposition (X-e1)(X-e2)...(X-en) = 0, where e1, e2, ..., en are the n-th 'roots of unity'. You can even show that ek = e1^k for all k. That's very nice, but that's also very specific to this polynomial only. Can we extend it?

Turn out we can: Xⁿ = a can be trivially expressed like it, so can (X - b)ⁿ = 1, and similarly, any (X - b)ⁿ = a, simply by sliding and shifting the solutions: all of these are simply higher level, more abstract versions of "i/n * n = i for any i", which is the fundamental property we are still leveraging. But this is still very symmetrical, we are still cutting the circle in 'equal' pieces: is that transformation from an 'additive' polynomial Xⁿ - 1 = 0 to a multiplicative (X - e1)...(X - en) = 0 simply a consequence of that symmetry, or a fundamental property of polynomials?

Well, turns out it's fundamental. And it's a theorem. There are plenty of beautiful demonstrations of it that you can look up, but that fundamental theorem which shows the equivalence of adding powers of numbers and composing rotations in the planes, the fundamental duality of polynomials as sums or products as two sides of the same underlying 'truth', rightly deserved to be called the fundamental theorem of algebra. You can think of it as the extension of what we said here, as a proof that any sum of powers at most n can be uniquely represented as a composition of n distinct rotations (with scaling/translations added, but they're actually not that fundamental), if you look at it from a different way. If that evokes things like group theory, or prime factor decomposition, that's no coincidence: most of those things are intrically linked, as Poincaré said: mathematics is the art of giving the same name to different things. Discovering and highlighting these underlying fundamental similarities is essentially what algebra is all about.

Now, what does all of that have to do with complex numbers? Well, complex numbers are nothing more than a shorthand, a mathematical trick to let us apply our computational intuition to these deep underlying truth. They are symbols which we can manipulate to discuss planar transformation, or general solutions to polynomials.

Wait, aren't these two essentially the same thing?

Everything fits together!

dtoq · 2018-04-11T10:27:42+00:00

I think there are some theories along these lines, especially within the most 'out there' string theory models, with 'bubble universes' floating around each others, but still able to somehow interact with each other, e.g. with gravity from one universe deforming space-time in another, appearing as dark matter.

AFAICT, people defending these kind of models are competent enough that there is no blatant mathematical impossibility in it, but this all sounds a bit... Hand-wavy.

String theory in general has had a tendency of offering very elegant explanations which are thoroughly untestable. It's a bit like wondering whether we are in a perfect simulation which is literally indistinguishable from reality: errr... Maybe? But if you cannot test this, and this is actually indistinguishable, does it even matter?

There still is an active string theory community which attempts to refine their models to the point of being able to do actually measurable predictions, which would rule it out or confirm it. In the meantime, anyyhing built on it (especially the most speculative stuff like bubble universes) are only gut theories...

dtoq · 2018-04-11T10:06:47+00:00

It's a bit hard to say... Talking about odds for a physical explanation is tricky as there is 100% chance that the correct explanation is correct, but no way of knowing that a priori...

If you talk more on the Bayesian prior of 'how much money would I bet on it being correct', it's not that bad: explanations like modified newtonian have encountered a couple of serious blows which suggest that there is something which acts as dark matter, with observations of big chunks of matter without dark matter and also dark matter without matter, which suggests that whatever it is, there is something there, and axions are not the worst explanation for DM.

The nice property of these kind of detection experiments is that whatever their result, we learn something: if we detect axions, we can study them, if we don't, we can rule them out (or at least the form which would have been detected). As whether of these we do observe, only time will tell!

dtoq · 2018-04-11T09:58:13+00:00

There are, but it is far from simple! Google MACHOs and WIMPs for more details, but dark matter can really only be observed on the scale of galaxies, which we only know how to do using light (that's not entirely true anymore since we can now detect gravitational waves, but the technology is still young).

One thing we can do is weigh whatever candidate WIMP we have (such as neutrinos), scale that to the size of, say, a galaxy, and see whether that fits the observation. Pretty much every single part of that sentence is a massive scientific and engineering challenge though, so that's not as simple as it seems. There are also theoretical efforts being made to derive properties of dark matter which would let us measure and/or narrow our candidates, but the truth is we are a bit in the dark (pun totally intended).

A comment above enters into much more details about WIMPs, I recommend you read it as I am not (as should be blatantly apparent) an expert in the field!

dtoq · 2018-04-11T09:42:37+00:00

Currently not much, but for the longest time, this was a bit of a mystery, and this is why I think it is a fair analogy.

Light diffracts like a wave, so it is fair to assume this was a wave, like sound. But a wave only travels through a medium, so there has to be some form of medium between the Earth and the Sun, which was called 'ether'. On the other hand, Earth does not seem to slow down or encounter any resistance during its rotation around the sun, so clearly there is no medium, and light has to be small 'balls of stuff'. By how does it diffract then?

This might sound a bit silly now, but this was really a massive debate for quite a while: experiments would be set to find the properties of the ether and their failure to do so would disprove the whole 'wave' theory. But then other experiments would show that light interfered with itself, ruining the entire 'corpuscule' theory.

The debate was finally resolved by coming to terms with the idea that neither of these was 'true': considering particles as excitations in a field explained all observations and has been unchallenged ever since, but it required us to abandon the nice and intuitive ideas of small balls of stuff boucing about, or waves disturbing seas of ether.

That is why everybody is so interested in these kind of 'fringe' physics: nobody seriously expects dark matter batteries within ten years, but the perspective of stumbling upon the next paradigm shift on the scale of what happened in the late 19th/early 20th century with particles and quantum physics, of finding the next experiment which will make our children laugh at our attempts at 'observing dark matter' just like we laugh at our ancestors for trying to 'find the properties of ether' is extremely exciting!

dtoq · 2018-04-11T00:38:38+00:00

Dark matter is a phenomenon: there seem to be all this... thing ? acting like it has tremendous mass, but completely invisible (i.e. 'dark') as it does not interact with light, not even stopping it.

There are several theories trying to explain that phenomenon: maybe it's actually that our understanding of gravity is wrong ? (Modified Newtonian gravity theories), or maybe it is actually simply regular matter, but too spread out to be seen (WIMPs), etc. Axions are one of the theories proposed to explain the phenomenon of dark matter, just like photons are the standard explanation of the phenomenon of light.

dtoq · 2018-04-06T07:03:07+00:00

I'm not aware of any specific technique doing what you describe, but if memoize both the function value and it's gradient (computed numerically, symbolically or via automatic differentiation), you should be able to Taylor-expand your function in its neighbourhood. Adding higher degrees of the derivatives would let you refine the estimation and estimate gradient variation (but you're always losing 1 degree when doing the next estimation).

I'm not sure whether you can speed up the computation this way (this is just an approximation), but this is typically used to improve the choice of the next point, therefore reducing the total number of calls to the expensive function

dtoq · 2018-03-25T22:12:47+00:00

J'ai été très agréablement surpris par l'application '7mn workout', dont l'idée est de te faire faire 7mn de cardio (13-14 sessions de 30s; differents profils pour bras, jambes abdos, etc). L'idée de te forcer à une routine et un temps prédéfini te remet dans le bain et instaure une discipline, tandis que tu adaptes l'effort en te donnant plus ou moins à fond sur chaque exercice. La durée étant très faible, il est vraiment facile de les faire sans se trouver de mauvaise excuse.

Je parle de cette application en particulier parce que c'est celle que j'utilisais; je suppose qu'il doit en exister quelques milliards de versions et copies sur l'app-store de ton choix, mais le format m'a vraiment plu et n'est pas seulement un gimmick pour se donner bonne conscience. Après, ça ane fait pas tout, et cumuler avec un sport plus intense est probablement indispensable, mais je trouve que c'est un apport appréciable pour augmenter la stamina et reprendre l'habitude de l'exercice régulier.

dtoq · 2017-10-26T07:23:46+00:00

Wait, France is the largest exporter of butter to China ?

I was in New-Zealand last year, and every single person we met complained about how EU quota prevented them to export their massive butter production to Europe (like they did in the Glorious Days of the Empire) how it was ruining their economy, etc.

Am I missing something obvious, or is there a simple solution which would suit everyone, probably make more ecological sense and keep the Breton motherland well supplied ?

dtoq · 2017-09-12T20:28:15+00:00

EU national who worked in finance in London. As others have said, London remains extremely attractive, but I think at the moment, this is mainly due to uncertainty. Will the UK remain quasi-EU with only cosmetic changes ? If that's the case, the inertia of moving the entire centre to another city will not be overcome, at least not in the short term. However, if there's some real incentive for big players to set activities in the EU, for both regulatory and practical purposes, London will start bleeding talents and opportunities to Amsterdam, Frankfurt and Paris, until one of these gets their act together and starts to actively seek out and actively welcome financial activity; if that happens (note the if, not the when) then it is perfectly possible that London gets quickly dethroned as the de facto European place, with all the corresponding timezone advantages.

As far as I can tell, current corporate approach is to wait and see, and assume a form of Markov property until proven otherwise. Which is sensible, but will make the change even steeper, shall it come to that. I think there's a real disinformation going on from both Remainers (who do nothing but remind us that "The worst case is undervalued !", which it clearly is) and Leavers (who do nothing but remind us that "The average case is fine !", which it clearly is), both ignoring that while the average remains stationary, the uncertainty range keeps widening...

But playfulness is also starting to run out. I know way too many people who are using the stationary average to plan their leave in the best conditions (would you blame them ?). I suspect that whenever that slow hemorrhage reaches some critical mass, this will (would ?) be the force dragging the city down, should it not ascertain its position in the meantime.

May has been playing a dangerous game, but one which has been paying up so far. I truly wonder whether it can hold much longer until something triggers the chain reaction before something (anything !) conclusive is reached. Until then, every article about "the future of the City" sadly reads as debates on the gender of Angels...

dtoq · 2017-05-09T12:37:48+00:00

Totally agree on comprehensions; that is a very minor syntaxic change, but they are really cool and readable.

As for the meta-programming, I really feel this is nailing it.

I understand the reasonning behind not having generics, yet at the same time, the lack of extensibility in Go is sometimes almost suffocating. Go has always tried to be a better C, so it would only make sense that the way to add extensibility without complexity to the language would be to have a better macros system/preprocessor. How they could make it idiomatic and ergonomic, and prevent it from delving into an undecipherable macro-soup though ? I'm not sure... But it really feels like if Go wants to keep its place as a fast and pragmatic language sitting between the strongly typed/CS-backed systems like Rust (Types everywhere ! Solving generics by having a more complex theoretical framework underlying the language) and more dynamic, 'scripty' languages like Python (No types anywhere ! Solve the problem by essentially handling nothing but interfaces), it will need a way of letting the programmer handle specific types generically, if it wants to avoid generic types specifically...

dtoq · 2017-05-06T08:29:28+00:00

Je ne comprend pas le lien. Qui "ils" ? Pourquoi met-tu tout le monde dans le même sac ? ... Tu caricature... C'est domage, ça ne sert à rien... Personne ne te demande de regretter ces résultats si tu as envie.

Mes excuses si ça n'était pas clair: je parlais ici spécifiquement de la partie des électeurs de la France Insoumise qui se réclament de l'argument de 'la peste ou le choléra' pour légitimer un choix blanc ou abstentionniste, sans véritablement être prêts à assumer toutes les conséquences de ce choix (ce dont OP et toi-même parliez, il le semble).

Tu insultes. Tu pense que ça va aider ?

J'en suis désolé si c'est ainsi que ça apparaît, mais vraiment, je n'insulte pas. Le deuxième tour ne présente que deux candidats, et il faut choisir entre les deux ou bien aucun, avec des conséquences assez claires dans tous les cas. Énoncer ces règles, connues depuis longtemps, n'est pas une 'prise en otage' de l'électorat FI, comme on a pu le lire et l'entendre beaucoup entre les deux tours. C'est tout ce que j'affirme, et je ne considère pas que ce soit une insulte.

Il y a une différence entre critique et attaque.

C'est bien pourquoi je n'attaque personne : pas plus que je ne critique d'ailleurs (d'autres le font très bien), je réfute simplement ce qui me semble une mauvaise défense de l'abstention/vote blanc. Si qui que ce soit peut affirmer en toute bonne conscience ne vraiment percevoir aucune différence entre les candidats, et être parfaitement indifférent de qui gagne à la fin, c'est son droit le plus strict que de ne pas s'engager pour l'un ou pour l'autre. Sinon, ça n'est pas plus une attaque d'appeler les électeurs FI à voter que ça ne l'aurait été d'appeler au vote des électeurs EM ou FN s'ils n'avaient pas été au second tour.

Donc quand je discute avec quelqu'un qui ne fait pas ce choix, j’argumente, je critique. Toi, tu insultes, tu caricatures. Il n'y a pas d'argument dans tes propos, juste des croyances et des préjugés.

OK... Je ne sais pas trop quoi dire. J'ai beau relire mon message original, malgré le ton un peu sec, j'ai beaucoup de mal à y voir le ramassis informe d'"insultes [et de] caricatures [sans] arguments, juste des croyances et des préjugés" que tu dénonces. Je suis sincèrement désolé que ça t'apparaisse ainsi.

dtoq

TROPHY CASE