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Posted by kscarlet 4 hours ago

Markets are competitive if and only if P != NP(arxiv.org)
187 points | 126 commentspage 2
madihaa 3 hours ago|
the same author 14 years ago. Markets are Efficient if and Only if P = NP and now Markets are competitive if and only if P != NP https://papers.ssrn.com/sol3/papers.cfm?abstract_id=1773169&...
apothegm 3 hours ago|
Which would in turn imply that markets cannot be simultaneously efficient and competitive.
AlotOfReading 4 hours ago||
The argument structure is interesting, and reminds me a lot of Solomonoff Induction, but constrained into NP by the assumptions. I'm not sure the front half is enough to support the back half of the paper arguing that the current LLM craze means firms are actually running collusion detection algorithms, even unintentionally.
dzink 4 hours ago||
When everyone uses AI to study the same indicators and figures out how the prices move with those indicators they all start investing at the same time and the prices move together. AI silently gets everyone on the same page.
nok22kon 4 hours ago||
next stage - a single AI which computes the "correct" price that everyone else agrees on, and instantly reprice all financial instruments without trading them, thus not paying transaction costs
hgoel 3 hours ago|||
I hate to make the worn out AI to RNG comparison, but this kind of simultaneous "collusion" is really like assuming that everyone is using the same RNG seed to make their calls.
Muromec 4 hours ago|||
Sounds like soviet communist Sci-Fi with a planned economy managed objectively by The Computer.
iwontberude 4 hours ago||
It’s a great excuse for collusion
moomin 4 hours ago||
I don’t think anyone in the business thinks that the markets are 100% efficient, just that they are sufficiently efficient that beating them is a genuinely hard job requiring heavy, expensive analysis.
danans 2 hours ago|
> just that they are sufficiently efficient that beating them is a genuinely hard job requiring heavy, expensive analysis

No expensive analysis is needed. Beating them just requires (1) having disproportionate capital to others, and (2) having disproportionate control (and therefore know in advance) whatever the markets are pricing.

It helps that there are enough believers (in the religious/cult sense) that markets are 100% efficient, that they will deny that any of that is happening - even while they lose their shirts to those who are doing the market manipulation.

glimshe 4 hours ago||
Markets are competitive if and only if P === NP!

Now seriously, I wonder if AI collusion/use in investments would add to the market inefficiency and create opportunities for observing investors.

astrodust 4 hours ago|
NP factorial sounds like NP-ultra-hard.
emil-lp 2 hours ago||
NP! should be something like NP^NP, which is well known to be Σ^2_P. Slightly larger, but still inside PH.
emil-lp 2 hours ago||
This paper has all the hallmarks of being crackpot with GPT.
debugnik 2 hours ago|
It builds on a similar paper from 2011 by the same author, though. They've just found something very specific that they enjoy analyzing.
estebarb 3 hours ago||
This is interesting. Adam Smith said "People of the same trade seldom meet together, even for merriment and diversion, but the conversation ends in a conspiracy against the public, or in some contrivance to raise prices."

The annoying part is that, as the same Adam Smith says, regulating industries would end up enforcing such assemblies, reinforcing the problem... after all, industries can share information via the market itself...

And proposed solutions end up being controversial: employees ownership, open source, paying taxes over stocks ownership... or just hoping that colluders will be broken by a randomly ocurring incumbent...

FailMore 4 hours ago||
Would anyone mind explaining what P and NP are?
dpweb 3 hours ago||
P and NP are classes of computational problems.

A problem in P can be solved in polynomial time - the computation required grows relatively slowly as the input size increases. Like sorting a list of numbers.

A problem in NP requires exponential time or greater, but a proposed solution can be verified quickly. For example, checking a completed Sudoku puzzle.

It is believed but unproven that all problems in NP are NOT in P.

calfuris 3 hours ago|||
A problem in NP can have a (positive) solution verified in polynomial time. That's it. Requiring more than polynomial time to solve isn't part of the definition, and in fact it's an open question whether any problems in NP require more than polynomial time to solve.

Every single problem in P is in NP. What is believed but unproven is that some problems in NP are not in P.

SoftTalker 3 hours ago||||
I have never really understood this, from the time it was first introduced to me in my undergraduate education nearly 40 years ago. It seems to boil down to saying "all unsolvable problems are not in the set of solvable problems" which seems like a tautology. I don't get why "P != NP" is considered so profound.

I feel like I have not yet found the proper explanation. Or I'm just too dense to get it.

program_whiz 3 hours ago||
Not sure you're wanting an explanation, but it comes down more to equivalent algorithms than rigid categories. For example there is a P algo to sort a list of numbers, but not to solve a sudoku (NP). However there is a polynomial algo to check sudoku (spaces ^ 2 if you check every space against every other space for rule violation).

However, the reason all NP algos are part of the same category is because you can solve any problem in NP by switching the problem into another problem in the same category and solving that. For example, you can turn sudoku into a graph coloring problem, which is also NP. You can turn sorting (P) into something like balancing a tree, which is also P.

The major question is "is there any algorithm that would allow us to change some NP problems into P problems, solve it, then use it for the original problem". E.g. could we take graph coloring and turn it into sorting a list of numbers?

So basically, if there is any way to bridge the two, then it might mean every NP problem is actually solvable by a P algorithm, under some transformation. This would be immense because it would completely change the way we solve those algorithms and greatly reduce compute costs.

While this seems far-fetched, realize that there are some problems that seem extremely expensive if done the naiive way, but are actually solvable in P. For example, you _could_ write an exponential sorting algo (try every element in every position), but clever people found a way to make it efficient (P). So its possible we just need the right algo to completely change the landscape of computing.

However, as you say, its almost self-evidently true that P != NP, but has never been proven so (to do so, we need to prove that no such algorithm can exist). But clearly, solving an exponentially complex problem using a O(log n) algo would be remarkable.

To take a concrete example, currently the best algos to exhaustively check a board game like chess or go are exponential (NP). Its easy to verify the winner, but its exponential to enumerate every possible move (e.g. 80^turns states). If we found a polynomial way to solve this (even by converting to something simplified), then it would mean we could exhaustively search chess polynomial to the number of moves (e.g. turns^100). This changes it from "cannot be done in the lifespan of universe" to "its possible with a powerful computer in measurable time". We already use heuristics and estimates to explore the exponential space in efficient time, so if we had a polynomial algo chess, markets, optimization, and other NP problems would be extremely efficient to solve.

bjourne 3 hours ago|||
NP contains P. You're thinking of NP-hard problems.
random3 3 hours ago|||
It's a vast generalization of the cost to verify a problem/solution.

- P means polynomial - NP means nondeterministic polynomial

Roughly polynomial (P) represents the upper bound of the cost to verify, and the polynomial characterization says that given a problem with a certain input (e.g. the input can be the number of training examples in ML training set or the number of constraints/conditions in a general problem— e.g. all the places you want to visit on your next trip, given many "wants" in a group)

When the cost is polynomial relative to the input size it means it can only be finitely larger than the input - that's a characteristic of the polynomial which is just a finite sum of powers of x (the input).

When the cost is nondeterministic polynomial, one way to think about it in what is called a nondeterministic Turing machine. The nondeterministic part refers to the "states" that the machines can transition to from any current state. When the transition can happen to more than one state, we say it's non-deterministic— and can imagine it's determined by some probability.

The general assumption is that polynomial (P) is easier than nondeterministic polnomial (NP). This isn't necessarily the case as there can be arbitrarily large finite numbers (making P solutions intractible)

The P vs NP problem is one of the main open problems and generally considered a crank magnet and general confusion. For a good (likely the best) resource see https://scottaaronson.blog/

PandaRider 4 hours ago|||
I have taken algorithms courses.

This video explains in detail: https://www.youtube.com/watch?v=YX40hbAHx3s

In short, P means Polynomial time (i.e. markets can solve computation problems efficiently) and NP means Non-Deterministic Polynomial time (i.e. markets can verify solutions of computation problems efficiently but solutions are found by luck).

If P != NP, it means luck CANNOT be engineered and markets are competitive.

super_mario 4 hours ago|||
Wikipedia is a good source on this

P complexity class

https://en.wikipedia.org/wiki/P_(complexity)

NP complexity class

https://en.wikipedia.org/wiki/NP_(complexity)

P vs NP question

https://en.wikipedia.org/wiki/P_versus_NP_problem

VMG 4 hours ago|||
well obviously N=1
convolvatron 4 hours ago||
in CS we define a complexity class as a set of problems that have the same growth characteristic. that is for a problem size N, how long does it take in the worst case to find the solution for that problem.

one such class is the Polynomial class, or P, where the time to solution is some fixed exponent of N (like N^2, or 3).

the next big step is NP, which require a polynomial number of nondeterministic steps, whose solution can only be verified in polynomial time. usually solutions to NP problems are exponential in cost with respect to N (like 2^N), but thats not part of their definition.

problems in NP are generally identified by mapping them into a well known problem known to be in NP, where the mapping has to occur in polynomial time.

its an open question as to whether NP as a class can actually be solved in P time, but most people doubt that that is really the case.

api 4 hours ago||
If markets were perfectly efficient, entrepreneurship would not exist. An entrepreneur is, at this level, someone who looks for an arbitrage opportunity in correcting a market inefficiency, usually of the form "there is a market for X, X could be provided, but X is not currently provided."
AaronAPU 4 hours ago||
That seems to stretch the meaning of market inefficiency. Is the lack of unlimited free energy an inefficiency in a market? Because an entrepreneur who achieves that is going to do pretty well. I’d say that would be creating value not optimizing market efficiency.
edot 3 hours ago|||
Yeah, and arbitrage. Arbitrage is exploiting the difference in prices of the same asset between two markets. Arbitrage is also risk-free or darn close to it. Entrepreneurship is anything but. Arbitrage is not "gee this product doesn't exist, I'll start a company and invent it and manufacture it and sell it" ...
SoftTalker 3 hours ago|||
How would creating unlimited free energy allow an entrepreneur to do pretty well? It it's free, there's no money to be made.
xxpor 4 hours ago|||
Seems like t is a very critical variable then. For example, you could imagine a particular market is "perfectly" efficient at the moment (however you want to define the boundaries of a particular market), and there is no opportunity. But then a completely unrelated company or university makes a fundemental advancement in materials science that fundamentally changes the landscape. An exogenous shock in other words.

In a certain sense I guess this is why every anti-trust suit fundamentally comes down to defining the market bubble more than anything else.

ThrustVectoring 3 hours ago|||
In perfectly efficient markets, arbitrage gets paid exactly as much as it costs to discover and execute the arbitrage. Entrepreneurs would still exist, they would just be ambivalent between finding new arbitrage opportunities and seeking market-rate employment for their skills in finding arbitrage.
jayd16 3 hours ago||
Ok so the market is perfect... but I exist and have labor to provide. Am I not naturally an "inefficiency" by not participating in the market? Therefore by participating alone, I have a new wrinkle to work from?
kibwen 4 hours ago|
Keeping in mind the mistake in the HN title (should be "P != NP"), the interesting part of the abstract is this:

> Combined with Maymin (2011), who proved that market efficiency requires P = NP, this yields a fundamental impossibility: markets can be informationally efficient or competitive, but not both.

(Note that Maymin is the author of both papers.)

marcosdumay 4 hours ago||
Yet neither paper seems to eliminate the case of markets being neither. So both titles are incorrect.
iwontberude 4 hours ago||
Yeah using time complexity for computers to describe markets is simultaneously awesome and stupid.
marcosdumay 3 hours ago||
The idea that markets are an optimizing algorithm is kinda old already, and well established.

Both papers seem to be jokes about it, based on complete caricatures of competitiveness and efficiency. It's kinda like a recent paper that was posted here proving "general intelligence" impossible while ignoring that humans exist.

argv_empty 4 hours ago||
Except Maymin 2011 fails to even establish that his narrow definition of "markets are efficient" (specifically, finding a profitable technical analysis) is actually in NP.
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