HNHacker News
TopNewBestAskShowJobs

luca3v

70 karma · joined July 16, 2012

submissionscomments
luca3v··on Researchers have found a faster way to do integer linear programming
They prove a new upper bound to a combinatorial quantity that controls the worst-case running time of an algorithm of Dadush, not an upper bound to the optimal value of a given ILP instance.

If they wanted to see their ideas work in practice, they could implement Dadush's algorithm in light of these new bounds, but this would be unlikely to outperform something like CPLEX or Gurobi with all their heuristics and engineering optimizations developed over decades.

Otherwise, and this is the sense of the quoted sentence, they could go deep into the bowels of CPLEX or Gurobi to see if their ideas could yield some new speed-up on top of all the existing tricks, but this is not something that makes sense for the authors to do, though maybe someone else should.

luca3v··on Hacker News' favorite Xkcd comics (2022)
I would have guessed "Dependency" https://xkcd.com/2347/, but it did not even make the top 10
luca3v··on The curious case of the Raspberry Pi in the network closet (2019)
Somewhat relatex XKCD: https://xkcd.com/2730/
luca3v··on Coastline paradox
The exponential curve does look like a line when you zoom in very close to a point. For example, f(x) = e^x looks linear with slope e^x near x. You can see that, for small epsilon, e^(x+epsilon) - e^x is approximately epsilone^x, with an error term of the order of epsilon^2 e^x
luca3v··on Banks use your deposits to loan money to fossil-fuel, emissions-heavy firms
The analogy would be that if your friend Bob asks you for a $1k loan, you could tell him "done, I am loaning you $1k and for now I am keeping it safe for you; just tell me when you need it".

Now you have all the money you had before, and you friend "has" an extra $1k, so you have "created" money.

If Bob then tells you hey, I need the $1k to give it to John, you say no worries, and you go to John and says hey, here is $1k from Bob, and for now I am keeping it safe for you; just tell me when you need it. And so on.

If at some point John actually wants the $1k in cash then you actually give him the money, you cannot create it. Maybe at some point you have just $1k of real cash with you, other people owe you $9k, and yet other people have $10k of "created" money that you are keeping for them. If all of the latter want their money in cash, you are going to be in trouble.

Same with a bank, if a lot of depositors want their money back, the bank has to give it out of its reserves, it cannot "create" it to give it to them, hence the phenomenon of "runs on the bank" (because at any given time, the sum of all depositor balances in a bank is a lot more than the actual reserves) and why we need a federal insurance program to protect depositors.

luca3v··on Pricing Americans with finite-difference
You can see that the market deviates from the model and accounts for the fact that the Brownian motion model of Black-Scholes underestimates the probability of big moves: typically, options for the same security and the same expiration date have different IV, with options ATM having a lower IV and options deep ITM or deem OTM having larger IV.

If the market believed in the model, options for the same security and the same expiration date would all have the same IV, which would be whatever volatility the market thinks the security is going to have.

luca3v··on The economics of all-you-can-eat buffets (2020)
I don't think that this is how it works. In Italy almost all sushi restaurants are run by Chinese immigrants, but we definitely don't think of sushi as Chinese food.
luca3v··on Chicken hypnotism
The article ends with a reference to Trout Tickling, https://en.wikipedia.org/wiki/Trout_tickling, that sounds like some kind of Urban Dictionary euphemism, but is instead exactly what it sounds like
luca3v··on The diamond world takes radical steps to stop a pricing plunge
I understand that diamonds are the kind of Veblen goods for which people are willing to spend a lot of money because they are expensive, in a logic-defying circular way, and that the presence of a cartels- makes prices artificially high, but there are still two things that I can never wrap my head around:

1) That if someone wants to sell a used diamond, they get pennies on the dollar. It's reasonable that they would sell at a small discount compared to wholesale prices, because of the extra work of authenticating it, the small volume etc., but the difference is so great that one assumes that some businesses would step in and take advantage of the arbitrage opportunity

2) That there is any difference at all in prices between mined and lab-grown diamonds. They are literally the same material, and lab-grown diamonds are as "real"as the mined ones

Just consider gold. You can sell used gold at a small discount compared to spot prices, and if there was a cheap way to make "lab grown" gold, I am sure it would sell at exactly the same price as mined gold

luca3v··on An update on the campaign to defend serious math education in California
I don't know if it's still there in the revision, but in chapter one of the earlier draft of the California framework it said, in a prominent place "we reject ideas of natural gifts and talents"

Edit: in the new version it has been changed to "high-level mathematics achievement is not dependent on rare natural gifts, but rather can be cultivated"

luca3v··on One Hundred Prisoners Problem
If one player picks 50 of boxes, the probability of finding a particular number will be 50% independently of the strategy.

(Note that sum([1.0/(100-n) for n in range(70)]) is more than one: the probability is 1/100 + 99/100 * 1/99 + ... which adds 1/100 in each try)

The point of the cycle strategy is that there is at least a 30% probability that all 100 people will succeed, while this should intuitively happen only with probability (1/2)^100 which is inconceivably small.

luca3v··on Typography of 2001: A Space Odyssey (2014)
I am feeling really dumb for asking: the punchline of the comic is clearly that there is something terribly wrong with the typesetting of the business card, but what is it?
luca3v··on China’s noisy ‘dancing grannies’ silenced by device that disables speakers
It's probably some kind of universal remote
luca3v··on The Third Revolution in Warfare
https://outline.com/yZRf7g
luca3v··on Money creation in the modern economy (2014) [pdf]
Yes, this is correct! But some people, and perhaps not the grandparent comment, understand the "money creation" point as that money can be replicated infinitely, that is a bank get $1 mil deposit and makes $10 mil loans, and those loans, if deposited, could lead to $100 mil loans and so on
luca3v··on Money creation in the modern economy (2014) [pdf]
This is not exactly how fractional reserve banking works. I think that there is a misconception that if, for example, there is a bank regulation that allows 10% fractional reserve banking, then if a bank has $1 million in deposits (of actual cash that people gave to the bank to put in their checking accounts) the bank can make $10 million in loans, with $9 million being "created out of thin hair". In fact, if a bank has $1 million in deposits it can make only $900k in loans.

Indeed, suppose you are a bank and you have $1 mil in deposits, which you keep as reserve with the central bank. Now someone asks for a $900k loan. Now you have $1.9 mil in deposits ($1.9 mil liabilities), and you have $1 mil kept with the central bank in cash, and $900k owed from the guy with the loan (total $1.9 mil in assets, it checks out).

Now the guy with the loan withdraws his $900k to pay for his house or whatever; the bank gives him the $900k from the cash account it has at the central bank. Now the bank has $1 mil in liabilities (the checking accounts of the depositors), $100k in cash with the central bank, and $900k owed from the guy with the loan. Everything still checks out, but now the cash on hand is just $10% of the assets. The bank has reached the fractional reserve limit, and it is not allowed to make any more loans.

luca3v··on Working at a startup is overrated, both financially and emotionally
$200k is your expected equity payoff if you have a 2% chance that your equity is going to be worth $10M and a 98% chance that it's going to be worthless, which is the simplified model used in that back-of-the-envelope calculation
luca3v··on I'm Wil Wheaton. I Live with Chronic Depression and Anxiety. I Am Not Ashamed
SMBC: https://www.smbc-comics.com/comic/time-machine