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The universal weight subspace hypothesis

arxiv.org

81–90 of 146 posts

Re: The universal weight subspace hypothesis

#81

What's the relationship with the Platonic Representation Hypothesis?

I hope someone much smarter than I answers this. I’ve been noticing an uptick platonic and neo-platonic discourse in the zeitgeist and am wondering if we’re converging on something profound.

I've been noticing that as well....

Re: The universal weight subspace hypothesis

#83
post #77

This seems confusingly phrased. When they say things like "500 Vision Transformers", what they mean is 500 finetunes of the same base model, downloaded from the huggingface accounts of anonymous randos. These spaces are only "universal" to a single pretrained base model AFAICT. Is it really that surprising that finetunes would be extremely similar to each other? Especially LoRAs? I visited one of the models they refe…

Why would they be similar if they are trained on very different data? Also, trained from scratch models are also analyzed, imo.

They are trained on exactly the same data in the same order with the same optimizer because they are literally the same base model. With a little fine tuning added on top.

I see now that they did one experiment with trained from scratch models. They trained five Resnet-50s on five disjoint datasets of natural images, most quite small. And IIUC they were able to, without further training, combine them into one "universal" model that can be adapted to have only somewhat worse performance on any one of the five datasets (actually one of them is pretty bad) using only ~35 adaptation parameters. Which is kind of cool I guess but I also don't find it that surprising?

I don't expect that you'd get the same finding at large scale in LLMs trained from scratch on disjoint and dissimilar data with different optimizers etc. I would find that surprising. But it would be very expensive to do that experiment so I understand why they weren't able to.

Re: The universal weight subspace hypothesis

#84

Earlier quoted context omitted.

> So, they found an underlying commonality among the post-training structures in 50 LLaMA3-8B models, 177 GPT-2 models, and 8 Flan-T5 models; and, they demonstrated that the commonality could in every case be substituted for those in the original models with no loss of function; and noted that they seem to be the first to discover this. Could someone clarify what this means in practice? If there is a 'commonality' wh…

Prior to this paper, no one knew that X existed. If this paper proves sound, then now we know that X exists at all . No matter how large X is, one copy of X baked into the OS / into the silicon / into the GPU / into CUDA, is less than 50+177+8 copies of X baked into every single model. Would that permit future models to be shipped with #include as line 1? How much space would that save us? Could X.model be baked into…

If even remotely fact what you suggest here, I see two antipodal trajectories the authors secretly huddled and voted on:

1. As John Napier, who freely, generously, gifted his `Mirifici' for the benefit of all.

2. Here we go, patent trolls, have at it. OpenAI, et al burning midnight oil to grab as much real estate on this to erase any (even future?) debt stress, deprecating the AGI Philospher's Stone to first owning everything conceivable from a new miraculous `my precious' ring, not `open', closed.

Re: The universal weight subspace hypothesis

#85

> Principal component analysis of 200 GPT2, 500 Vision Transformers, 50 LLaMA- 8B, and 8 Flan-T5 models reveals consistent sharp spectral decay - strong evidence that a small number of weight directions capture dominant variance despite vast differences in training data, objectives, and initialization. Isn't it obvious?

This general idea shows up all over the place though. If you do 3D scans on thousands of mammal skulls, you'll find that a few PCs account for the vast majority of the variance. If you do frequency domain analysis of various physiological signals...same thing. Ditto for many, many other natural phenomena in the world. Interesting (maybe not surprising?) to see it in artificial phenomena as well

It's almost an artifact of PCA. You'll find "important" principal components everywhere you look. It takes real effort to construct a dataset where you don't. That doesn't mean though, for instance, that throwing away the less important principal components of an image is the best way to compress an image.

Re: The universal weight subspace hypothesis

#86

This seems confusingly phrased. When they say things like "500 Vision Transformers", what they mean is 500 finetunes of the same base model, downloaded from the huggingface accounts of anonymous randos. These spaces are only "universal" to a single pretrained base model AFAICT. Is it really that surprising that finetunes would be extremely similar to each other? Especially LoRAs? I visited one of the models they refe…

I agree - the results on the finetunes are not very surprising. The trained-from-scratch ResNets (Figure 2 and Section 3.2.1) are definitely more interesting, though somewhat limited in scope.

In any case, my impression is that this is not immediately more useful than a LoRA (and is probably not intended to be), but is maybe an avenue for further research.

Re: The universal weight subspace hypothesis

#87
post #77

This seems confusingly phrased. When they say things like "500 Vision Transformers", what they mean is 500 finetunes of the same base model, downloaded from the huggingface accounts of anonymous randos. These spaces are only "universal" to a single pretrained base model AFAICT. Is it really that surprising that finetunes would be extremely similar to each other? Especially LoRAs? I visited one of the models they refe…

Why would they be similar if they are trained on very different data? Also, trained from scratch models are also analyzed, imo.

I think there's two maybe subtle, but key concepts you're missing.

  1) "pertaining"
  2) architecture
1) Yes, they're trained on different data but "tune" implies most of the data is identical. So it should be surprising if the models end up significantly different.

2) the architecture and training methods matter. As a simple scenario to make things a bit easier to understand let's say we have two models with identical architectures and we'll use identical training methods (e.g. optimizer, learning rate, all that jazz) but learn on different data. Also to help so you can even reproduce this on your own let's train one on MNIST (numbers) and the other in FashionMNIST (clothing).

Do you expect these models to have similar latent spaces? You should! This is because despite the data being very different visually there are tons of implicit information that's shared (this is a big reason we do tuning in the first place!). One of the most obvious things you'll see is subnetworks that do edge detection (there's a famous paper showing this with convolutions but transformers do this too, just in a bit different way). The more similar the data (orders shouldn't matter too much with modern training methods but it definitely influences things) the more similar this will be too. So if we trained on LAION we should expect it to do really well on ImageNet because even if there aren't identical images (there are some) there are the same classes (even if labels are different)[0].

If you think a bit here you'll actually realize that some of this will happen even if you change architectures because some principles are the same. Where the architecture similarity and training similarity really help is that they bias features being learned at the same rate and in the same place. But this idea is also why you can distill between different architectures, not just by passing the final output but even using intermediate information.

To help, remember that these models converge. Accuracy jumps a lot in the beginning then slows. For example you might get 70% accuracy in a few epochs but need a few hundred to get to 90% (example numbers). So ask yourself "what's being learned first and why?" A lot will make more sense if you do this.

[0] I have a whole rant on the indirect of saying "zero shot" on ImageNet (or COCO) when trained in things like LAION or JFT. It's not zero shot because ImageNet is in distribution! We wouldn't say "we zero shotted the test set" smh

Re: The universal weight subspace hypothesis

#88

It's basically way better than LoRA under all respects and could even be used to speed up inference. I wonder whether the big models are not using it already... If not we'll see a blow up in capabilities very, very soon. What they've shown is that you can find the subset of parameters responsible for transfer of capability to new tasks. Does it apply to completely novel tasks? No, that would be magic. Tasks that need…

> Does it apply to completely novel tasks? No, that would be magic.

Are there novel tasks? Inside the limits of physics, tasks are finite, and most of them are pointless. One can certainly entertain tasks that transcend physics, but that isn't necessary if one merely wants an immortal and indomitable electronic god.

Re: The universal weight subspace hypothesis

#90

I find myself wanting genetic algorithms to be applied to try to develop and improve these structures... But I always want Genetic Algorithms to show up in any discussion about neural networks...

That would be an excellent use of GA and all the other 'not based on training a network' methods, now that we have a target and can evaluate against it!

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