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#manifolds

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I have a really weird #ICanHazPDF request. I remember a #MathOverflow question about the classification of #manifolds in which a paper (apparently unpublished) was linked from the author's website. I think it was by either Manolescu or Nicolaescu and it was a very nice, short survey of the current state of the classification. I thought I had a copy of this, but I can't find it or the original MathOverflow question. I've tried DuckDuckGo, Yandex, Google, and Bing to no avail. It's not this (pi.math.cornell.edu/~hatcher/P) by Allen Hatcher. Did I hallucinate this survey article?

ManifoldsBase.jl 0.14.10 introduces an interface to implement `Weigarten(M, p, X, V)` maps (juliamanifolds.github.io/Manif).
Together with the new ManifoldDiff.jl 0.3.6 this allows for a generic implementation of a conversion from Euclidean to Riemannian Hessians for embedded submanifolds, see juliamanifolds.github.io/Manif. #Manifolds #Julia

juliamanifolds.github.ioBasic functions · ManifoldsBase.jl
Continued thread

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Addendae (cont'd)

Manifold hypothesis
en.wikipedia.org/wiki/Manifold

Many high-dimensional data sets (requiring many variables) in the real world actually lie along low-dimensional latent manifolds in that high-dimensional space (described by a smaller number of variables).

This principle may underpin the effectiveness of ML algorithms in describing high-dimensional data sets by considering a few common features.

en.wikipedia.orgManifold hypothesis - Wikipedia
bioRxivNeural manifolds in V1 change with top-down signals from V4 targeting the foveal regionHigh-dimensional brain activity is often organised into lower-dimensional neural manifolds. However, the neural manifolds of the visual cortex remain understudied. Here, we study large-scale multielectrode electrophysiological recordings of macaque ( Macaca mulatta ) areas V1, V4 and DP with a high spatio-temporal resolution. We find, for the first time, that the population activity of V1 contains two separate neural manifolds, which correlate strongly with eye closure (eyes open/closed) and have distinct dimensionalities. Moreover, we find strong top-down signals from V4 to V1, particularly to the foveal region of V1, which are significantly stronger during the eyes-open periods, a previously unknown effect. Finally, in silico simulations of a balanced spiking neuron network qualitatively reproduce the experimental findings. Taken together, our analyses and simulations suggest that top-down signals modulate the population activity of V1, causing two distinct neural manifolds. We postulate that the top-down modulation during the eyes-open periods prepares V1 for fast and efficient visual responses, resulting in a type of visual stand-by mode. ### Competing Interest Statement The authors have declared no competing interest.