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Hard problems that reduce to document ranking (noperator.dev)
318 points by noperator 479 days ago
15 comments

The open source ranking library is really interesting. It's using a type of merge sort where the comparator function is an llm comparing (but doing batches >2 for fewer calls).

Reducing problems to document ranking is effectively a type of test-time search - also very interesting!

I wonder if this approach could be combined with GRPO to create more efficient chain of thought search...

https://github.com/BishopFox/raink?tab=readme-ov-file#descri...

The article introducing the library has something about how pairwise comparisons are most reliable (i.e. for each pair of items you ask an LLM which they prefer) but computationally expensive. Doing a single LLM call (rank these items in order) is much less reliable. So they do something in between that gives enough pairwise comparisons to have a more reliable list.

https://news.ycombinator.com/item?id=43175658

One interesting thing about LLMs, that is also related to why chain of thoughts work so well, is that they are good at sampling (saying a lot of things about a problem), and are good, when shown N solutions, to point at the potentially better one. They do these things better than zero-shot "tell me how to do that". So CoT is searching inside the space of representation + ranking, basically. So this idea is leveraging something LLMs are able to clearly do pretty well.
This furthers an idea I've had recently that we (and the media) are focusing too much on creating value by making more ever more complex LLMs, and instead we are vastly underestimating creative applications of current generation AI.
Agree. I think LLMs are usually not "harnessed" correctly for complex, multi-step problems—hence the `raink` CLI tool: https://github.com/noperator/raink
Why not both?

The LLM companies work on the LLMs, while tens of thousands of startups and established companies work on applying what already exists.

It's not either/or.

Currently we are using mllms like lego blocks to build lego-powered-like devices.
A concept that I've been thinking about a lot lately: transforming complex problems into document ranking problems to make them easier to solve. LLMs can assist greatly here, as I demonstrated at inaugural DistrictCon this past weekend.
So would this be 1600 commits and one of which fixes the bug (which might be easier with commit messages?) or is this a diff between two revisions, with 1600 chunks, each chunk a “document” ?

I am trying to grok why we want to find the fix - is it to understand what was done so we can exploit unpatched instances in the wild?

Also also

“identifying candidate functions for fuzzing targets“ - if every function is a document I get where the list of documents is, what what is the query - how do I say “find me a function most suitable to fuzzing”

Apologies if that’s brusque - trying to fit new concepts in my brain :-)

Great questions. For commits or revision diffs as documents—either will work. Yes, I've applied this to N-day vulnerability identification to support exploit development and offensive security testing. And yes, for fuzzing, a sensible approach would be to dump the exported function attributes (names, source/disassembled code, other relevant context, etc.) from a built shared library, and ask, "Which of these functions most likely parses complex input and may be a good candidate for fuzzing?" I've had some success with that specific approach already.
Very cool! This is also one of my beliefs in building tools for research, that if you can solve the problem of predicting and ranking the top references for a given idea, then you've learned to understand a lot about problem solving and decomposing problems into their ingredients. I've been pleasantly surprised by how well LLMs can rank relevance, compared to supervised training of a relevancy score. I'll read the linked paper (shameless plug, here it is on my research tools site: https://sugaku.net/oa/W4401043313/)
Great article, I’ve had similar findings! LLM based “document-chunk” ranking is a core feature of PaperQA2 (https://github.com/Future-House/paper-qa) and part of why it works so well for scientific Q&A compared to traditional embedding-ranking based RAG systems.
That's awesome. Will take a closer look!
So instead of testing each patch, it's faster to "read" it and see if it looks like the right kind of change to be fixing a particular bug. Neat.
I'm curious - why is LLM ranking preferred over cosine similarity from an embedding model (in the context of this specific problem)?
Because the question "does Diff A fix Vuln B" is not answered by the cosine distance between vector(Diff A) and vector(Vuln B).
You can learn a function that embeds diffs with vulnerability A near each other, and vulnerability B near each other, etc which is much more efficient than asking an LLM about hundreds of chunks one at a time.

Maybe you even use the LLM to find vulnerable snippets at the beginning, but a multi class classifier or embedding model will be way better at runtime.

Perhaps you can learn such a function, but it may be hard to learn a suitable embedding space directly, so it makes sense to lean on the more general capabilities of an LLM model (perhaps fine-tuned and distilled for more efficiency).
In principle, there is no reason why an LLM should be able to do better than a more focused model, and a lot of reasons why it will be worse. You’re wasting a ton of parameters memorizing the capital of France and what the powerhouse of a cell is.

If data is the issue you can probably even generate vulnerabilities to create a synthetic dataset.

I've thought about this and am very interested in this problem. Specifically, how can you efficiently come up with a kernel function that maps a "classic" embedding space to answer a specific ranking problem?

With enough data, you could train a classic ml model, or you could keep the llm in the inference pipeline, but is there another way?

The typical methods would be

1. Train an embedding model which forces “similar” inputs close together using triplet loss. Here “similar” can mean anything, but you would probably want to mark similar vulnerabilities as being similar.

2. If you have a fixed set of N vulnerabilities you can train a multi class classifier. Of course it’s a pain in the ass to add a new class later on.

3. For any particular vulnerability you could train a ranking model using hinge loss. This is what most industrial ranking and recommendation systems do.

"does Diff A fix Vuln B" is not the ranking solution proposed by the author. the ranking set-up is the same as the embedding case.
What if u embed `askLLM("5 thins this Diff could fix" + chunk)` instead of `chunk`? That should be closer in the latent space.
Interesting insight, and funny in a way since LLMs themselves can be seen as a specific form of document ranking, i.e. ranking a list of tokens by appropriateness as continuation of a text sequence.
Ranking (information retrieval) https://en.wikipedia.org/wiki/Ranking_(information_retrieval...

awesome-generative-information-retrieval > Re-ranking: https://github.com/gabriben/awesome-generative-information-r...

Very interesting application of LLMs. Thanks for sharing!
I see in the readme you investigated tournament style, but didn't see results.

How'd it perform compared to listwise?

Also curious about whether you tried schema-based querying to the llm (function calling / structured output). I recently tried to have a discussion about this exact topic with someone who posted about pairwise ranking with llms.

https://lobste.rs/s/yxlisx/llm_sort_sort_input_lines_semanti...

Hum... The gotcha is that LLMs can rank for subject relevance, but not for most other kinds of quality.
What other kinds of quality are you thinking of?
I'll be happy when I meet an LLM that doesn't randomly inject/ignore the word "not".
That title hurts my head to read
Minor nitpick,

Should be "document ranking reduces to these hard problems",

I never knew why the convention was like that, it seems backwards to me as well, but that's how it is.

"Document ranking reduces to these hard problems" would imply that document ranking is itself an instance of a certain group of hard problems. That's not what the article is saying.
I know its counterintuitive, as I explained in my comment, but that's the correct terminology in CS world.
I want to hear more about your point of view, because I disagree and am curious if there's another definition of "reduce". In my CS world, reduce is a term that you use to take a list of stuff and return a smaller list or instance of stuff. For example: [1, 2, 3].reduce(+) => 6. The title would go like [hardProblem1, hardProblem2, hardProblem3].reduce(...) => documentRanking. I think this mental model works for the non-CS world. So I'm curious what your viewpoint is.
In (Theoretical) Computer Science it is sometimes helpful to be able to say "Any instance of an A-type Problem can be transformed into an instance of a B-type Problem by applying this polynomial-time procedure".

Say you have a problem that you know reasonably well (A-type) and another one that you're studying (B-type), intuitively, you'd say "If I transform B to A and I know the solution to A, then I solved B" but what you actually need to do is to transform A to B, this is called "reducing A to B", for some reason, and then you can say things like "B is at least as complex as A" and "I can solve some instances of B the way I solve the general case of A".

This doesn't really apply here since neither the "hard problems" TFA mentions nor "document ranking" are canonical problems that you would typically use in these proofs, but since he's borrowing the term from this part of CS I wanted to make that remark on its proper use. Hence why I wrote "minor nitpick".

The reduce operation that you mentioned doesn't make sense within the context of the article.

Wikipedia: “Intuitively, problem A is reducible to problem B, if an algorithm for solving problem B efficiently (if it existed) could also be used as a subroutine to solve problem A efficiently.”

The article takes for granted that LLM-driven listwise comparisons efficiently solve document ranking (problem B), and then shows this can also be used as a subroutine to solve various hard problems like vulnerability analysis (problems A) efficiently.

If A reduces to B, it means that an algorithm implementing B can be used (with some pre- and post-processing) to solve A.

If A reduces to B, it means that B is at least as hard as A.

This is the standard terminology in every theoretical computer science; see for example the DPV textbook on page 210: https://github.com/eherbold/berkeleytextbooks/blob/master/Al...

Isn't that what I wrote on [1]?

Do you have something to add or is it just ... a confirmation?

Weird.

1: https://news.ycombinator.com/item?id=43179918

Are you trolling or what. Let's see what's written in the comment above.

> If A reduces to B, it means that an algorithm implementing B can be used (with some pre- and post-processing) to solve A.

Here we say that that we can solve a "hard problem" if we can express it in terms of the "Document Ranking" problem.

Let's rewrite that quoted sentence:

An algorithm implementing "Document Ranking" can be used (with some pre- and post-processing) to solve "Hard problem".

Let's do substitution in the first part of the sentence, "If A reduces to B", where A is "hard problem" and B is "Document Ranking":

Hard problem reduces to Document Ranking.

That means EXACTLY that we can USE Document Ranking to SOLVE the Hard Problem. Just as we wanted.

No, that is not what you wrote. You wrote “document ranking reduces to these hard problems", which means that document ranking can be solved with an algorithm for one of those hard problems. The article discusses the opposite: those hard problems can be solved by using algorithms for document ranking (which is itself a non-trivial problem)
Not quite - in complexity theory you say problem A reduces to problem B if an oracle for problem B can be used to solve problem A. So the title of the article is correct, as an oracle for document ranking (LLMs in this case) can be used to solve a list of hard problems (given in the article).
Wrong.

At least bother to read the discussion in the sibling comments.

It's standard terminology. I'm not going to waste time arguing about it.
Define what's an oracle for you, that's a concept that's not even needed for this discussion.

I don't think you understand what is being talked about here.