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by oakridge 1659 days ago
My question is how much of the operations in JAX here can be done with reduced precision and can utilize training accelerators i.e. TPUs. I've noticed a lot of research coming out in physics, where everything is simulated in at least double float, being augmented with ML approaches where precision is traded for dynamic range.
2 comments
dionhaefner 1659 days ago
The thing with reduced precision is that things may look fine at first, but then you eventually notice unphysical features in your solution (like additional wave modes after very long simulation times, or energy conservation issues). So we really don't know as a community yet how far we can venture from float64, but it looks like float32 may be viable.

Veros works OK on TPUs (about the same speed as a high-end GPU), but since you can't buy TPUs that's an immediate no for most academic users of climate models. Renting hardware doesn't really make sense when you keep it busy for months at a time and the HPC infrastructure is already in place.

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adgjlsfhk1 1659 days ago
can't you fix a lot of the nonphysical issues by using better integration schemes? that might be hard in Jax though. From what I know, it's options for better numerical stability are pretty limited.
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ChrisRackauckas 1659 days ago
No, in fact, you want to go lower order with lower precision. The real answer is that if the solution is in the chaotic regime then maybe Float16 is fine because you'll be dominated by other numerical errors anyways (if you're also making sure you have adequate conservation so the solution doesn't explode in some way), but if you're not in the chaotic regime then even Float32 is pushing it in many cases (i.e. it better be non-stiff as stiffness pretty much guernetees operations which span beyond Float32 relative epsilon). So it's a case-dependent topic and not something that has an easy answer, though the case for Float16 is rather small.

(We had some small tests generating TPU ODE solver code from Julia and showcased some rather bizarre stuff back when Keno was working on it, but never wrote a post summarizing all of it)

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adgjlsfhk1 1659 days ago
I would recommend checking out https://www.youtube.com/watch?v=GiSsoA1udUk. It shows that you can can do climate models with 16 bit numbers.
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