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lgdw

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Arnold's Cat Map

en.wikipedia.org
1 points·by lgdw·3 tahun yang lalu·0 comments

Show HN: Web Tool for Training Music Soft-Skills

dwlg00.github.io
3 points·by lgdw·4 tahun yang lalu·0 comments

Ask HN: Trying to find a specific math book

4 points·by lgdw·4 tahun yang lalu·5 comments

comments

lgdw
·3 tahun yang lalu·discuss
Having a hard time following the lower bound proof, especially this part:

> By the definition of 𝑃𝑎 , we know there are at least as many programs in 𝑃𝑎 as there are artefacts in 𝜋 (𝐺), i.e. |𝑝𝑎 | ≥ #𝜋 (𝐺).

I'm not sure how the definition of P_a leads to |p_a| >= #\pi(G)...
lgdw
·3 tahun yang lalu·discuss
fifth one down.
lgdw
·3 tahun yang lalu·discuss
I remember this being in a NACLO problem last year.
lgdw
·4 tahun yang lalu·discuss
I'm not very familiar with physics, but if I recall correctly the electromagnetic force can be thought of as a Hopf fibration.
lgdw
·4 tahun yang lalu·discuss
Although it would depend on what kind of fields of math you are interested in (algebra, analysis, topology, etc), I think that you can't really _go wrong_ per se by learning Category Theory first, even if many of the examples/uses of category theory won't make sense at first. Of course, learning Category Theory first is definitely unorthodox; at least in college, you usually first learn basic algebra (Abstract Algebra, Linear Algebra) along with analysis (Complex Analysis, Real Analysis) and "advanced calculus" (Differential Equations, Multivariable Calculus). Fields like Category Theory usually come after that and are taught mostly in grad school, but at its core learning Category Theory doesn't require knowing a lot of prerequisites so I think in terms of accessibility it resides alongside fields like Linear Algebra or Group Theory. An advantage of learning Category Theory first is that once you have a decent grasp of it, you'd have the mathematical vocabulary to describe concepts learned in different fields; a homotopy is a 2-morphism in the category of topological spaces, for example.

That being said, if you like algebra the most, learn algebra first. If you enjoy topology, learn topology. There really isn't a "right place" to start with mathematics, and as long as you avoid fields of math that build heavily on other fields of math like K-theory or representation theory, you'll have a decent starting background in math. Most fields of math, not just Category Theory, have analogues to other fields (and Category Theory acts only to really formalize this connection), so you can't really go wrong with starting with something like Linear Algebra or Group Theory.
lgdw
·4 tahun yang lalu·discuss
Sorry, force of habit.
lgdw
·4 tahun yang lalu·discuss
Yes, this textbook is a great introduction to point-set topology. I'm not very familiar with algebraic topology so I can't comment on anything regarding that. I did learn a fair bit of category theory that I didn't know prior, like a formal explanation of deriving the Yoneda Lemma (I read this book before I read CWM). I think it's definitely possible to learn category theory from this book, especially if you already have a strong intuition for Topology.
lgdw
·4 tahun yang lalu·discuss
I forgot to add that Algebra Chapter 0 takes a similar (albeit slightly different) approach of teaching Abstract Algebra in terms of Category Theory. I don't have a link right now but I'm sure you can find it on libgen. (I've only read the first few chapters of Algebra Chapter 0 yet, but from what I've heard the rest of the textbook is as good as the first bit.)
lgdw
·4 tahun yang lalu·discuss
While I was in highschool I attended a lecture by David Spivak on a whim and was fascinated by the field ever since. Before really discovering Category Theory, I was more interested in low-level computer architecture and design (although I'm not very knowledgeable by any means) so I didn't really encounter Category Theory through the means that most Computer Science people do (FP, Haskell, etc). Once I learned Category Theory I became more interested in other fields of math.
lgdw
·4 tahun yang lalu·discuss
iirc it is just a mirror of libgen.
lgdw
·4 tahun yang lalu·discuss
Great textbook, I learned all the topology I know from it. Previously, Category Theory was taught as a field that connects branches of math, and thus in terms of other concepts. But recently there's a movement to view Category Theory as the definitive underlying field of math (instead of set theory), and teach different fields of math in terms of Category Theory rather than vice versa (a new-new math in a sense). I learned Category Theory well before learning abstract algebra and topology, and the embedding of Topology in Category Theory was seamless and intuitive; I feel as though this book proves that this new CT-centric view of math education has merit.

One of the authors, Tai-Danae Bradley, also runs math3ma [1] and is a prominent figure in Applied Category Theory. I had the pleasure of hearing her talk, and her way of explaining abstractions is very easy to understand despite Category Theory being fairly obtuse at times (looking at you, Mac Lane!)

Also, an obligatory shilling of the Topos Institute [2]. They're a research institution based in Berkeley, and they have weekly talks on Category Theory that they release on youtube. If you're interested in the categorification of mathematics, you need to check them out.

[1] https://www.math3ma.com/

[2] https://topos.site/
lgdw
·4 tahun yang lalu·discuss
It's the actual process of translating everything into boxes and arrows that's the core of ACT.
lgdw
·4 tahun yang lalu·discuss
Yes, that's why I recommend starting out with 7 Sketches.
lgdw
·4 tahun yang lalu·discuss
If anyone is interested in Applied Category Theory, definitely check out the Topos Institute in Berkeley [1]. They do weekly seminars that they post on youtube and a really intriguing blog. I must say that David Spivak is a treasure to hear speak. 7 Sketches in Compositionality [2] was my introduction into Category Theory (written by Spivak and Brendan Fong, another member of Topos), and it really sold the idea of Category Theory as a field that's not just a mathematical meta-language but also a field that can stand on its own. I recommend it over Mac Lane's CWM if you're not a mathematician.

[1] https://topos.site/ [2] https://arxiv.org/abs/1803.05316
lgdw
·4 tahun yang lalu·discuss
Yes, it's this one! Thank you so much.
lgdw
·4 tahun yang lalu·discuss
Very interesting but I think the original thread was at least a month ago.