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by derefr
598 days ago
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So, I'm just a layman when it comes to AI/ML, but I do understand computability — what's possible to do with a given machine, and how we can build higher-computational-power primitives out of lower-computational-power primitives by plugging those primitives together with "glue" like parallel feed-forward chains (e.g. an ALU adder's carry bits) and loops over static sub-states of execution. My own mental model for what Transformers must necessarily be doing, in order to be able to compute what they compute, given: 1. the primitives they're made of (for Transformers: matmul a learned matrix; vector-add a learned bias vector; normalize; softmax) 2. what those primitives can compute over a single layer 3. the low-ish total number of layers in a Transformer model ...is that they were already effectively "state space models" in practice. So this doesn't really surprise me! (To be explicit, my assertion is that, for a given latent space between layers N and N+1 in a Transformer model, that latent space encodes a set of state variables [think CPU registers] used by the Nth serial computation steps of an arbitrary set of learned algorithms — where these algorithms are limited to those where every computation step is possible to encode in the form of a fused-matmul-plus-vadd, such that the algorithm itself can be learned as a depthwise-extruded sequence of weights across the layers; and where the learned algorithms can and do share state variables, both as inputs and as outputs; and where these state variables are all attenuated by an activation probability [in a Transformer: attention] such that the algorithms' outputs form a pre-multiplied conditional probability of the output given the confidence of the inputs — in turn such that the same state variable can be a low-confidence output for one algorithm, and a high-confidence output for another algorithm, and the high-confidence component of the output will swamp the low-confidence output.) |
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> While Transformers have been the main architecture behind deep learning's success in language modeling, state-space models (SSMs) such as Mamba have recently been shown to match or outperform Transformers at small to medium scale. We show that these families of models are actually quite closely related, and develop a rich framework of theoretical connections between SSMs and variants of attention, connected through various decompositions of a well-studied class of structured semiseparable matrices. Our state space duality (SSD) framework allows us to design a new architecture (Mamba-2) whose core layer is an a refinement of Mamba's selective SSM that is 2-8X faster, while continuing to be competitive with Transformers on language modeling.
https://arxiv.org/abs/2405.21060