Great video! The reason the golden ratio φ appears in the A5 representation is that the geometrical construction of a regular pentagon involves the construction of a line segment of length φ.

"we even teach matrices and linear algebra to cs students, so you know its not that bad" 🤣🤣🤣 Seriously though wonderful video, really gave me a better notion of what representations are. Thanks for this.

18:45 "We even teach matrices and linear algebra to CS students so you know it's not that bad" BASED

3:10 196,883 (the dimension of the smallest nontrivial representation of the monster)

I really like advanced topics made more accessible like this, but not any simpler than it should be. I only have a minor in math from uni and this was the perfect level for me, so thank you 😊

Good explanation, but I really wish you had mentioned that groups are required to be associative. It’s perhaps their most important property. Associativity is the only reason you’re allowed to think of the operation as a transformation so that representation theory makes sense. What you described is technically called a loop.

Isnt the group operation necessarily supposed to be associative as well?

I'm a CS student and I agree with the passing remark... they never push us hard enough.

Good video. However, I think at 11:19 you 'give up' on matrices a little too quickly. In fact, your choice of representation starting at 9:29 is already more complicated than it needs to be. A really useful and important fact -- especially for wrapping one's head around groups and/or representations -- is that: All finite groups are subsets of some Permutation (aka Symmetric) group. In other words: All groups can be represented as simple permutation matrices which *_only_* contain 0s and 1s! (Even more, each column contains exactly one 1, and each row also contains exactly one 1.) This is really useful, since permutation matrices are very simple to compute with and use as examples. For example, for C4 (at 11:19), you could simply use these 4 matrices: rho(0) = the identity matrix, [1000 0100 0010 0001] rho(1) = [0100 0010 0001 1000] rho(2) = rho(1)^2 = [0010 0001 1000 0100] rho(3) = rho(1)^3 = [0001 1000 0100 0010] These four matrices are a subset (subgroup) of S4 (the permutations of 4 objects). Yes, they require 4 dimensions, but they are incredibly simple. To reduce the number of dimensions, you have to do clever things like using negatives, nth roots, complex numbers, etc. That all takes cleverness to figure out. But if you just want to jump into groups/representations without needing a whole lot of background, using subsets of Sn (for appropriately sized n) to represent your group elements is the easiest way to do it. It allows you to get a representation that *works correctly* right away, without much fuss. And if you have a more 'reduced' representation that is hard to understand or that you screwed up some how, you can fall back to subsets of Sn as a kind of 'debugging' aid to help you understand how the group should really work. The only real drawback of using permutation matrices is that their dimensions are usually bigger than technically necessary. They can get out of hand for high-degree finite groups, but by that point you can start figuring out how to reduce your representations, and that's where all the complicated representation stuff starts happening. But you don't need that stuff right away! To prove my point, for A5 at 14:45, you could instead just use the subset of S5 directly as 5x5 permutation matrices. Example, kappa((345)) would just be: [10000 01000 00010 00001 00100] Now, isn't that much nicer to introduce to somebody just learning about representations than the monstrosity with all those negatives and 1/2's and phi's in the 3D representation? Just sayin'!

I loved watching this as a math enthusiast and programmer, please continue :)

Amazing, it's great how you emphasize the importance of maps to more than just functions

amazing video, that break with the birb was timed perfectly

This video was what made me start studying abstract algebra! Thanks for making it!

Besides all the other mistakes that were already pointed out (missing associativity in the definition of groups, confusing fields and vector spaces in the definition of GL_n(F) / GL(V), subset symbols instead of ∈ at 5:48...), the derivation of the symmetry group of the dodecahedron having 60 elements is also completely false - you overcount by counting rotations by 0° around different faces as different elements, as well as rotations around opposite faces, while completely neglecting rotations around vertices and edges (both of which leave no single face in its place, and aren't part of the rotations you already counted). Don't get me wrong, I appreciate that you've taken the time to make this video to help more people get into representations, and you definitely did do a lot of things right - but next time maybe have someone else take a second look over the script before making the video, otherwise mistakes like those will inevitably happen and distract from the knowledge you're actually trying to share.

Amazing first video, i am already introduced in the topic, but i can still feel how good of an introduction this video is, thank you for this educational piece.

The five cubes animation was great and seeing the dodecahedron was crazy.

The way this creator has begun to define his channel is hinting me towards an isomorphism to greatness.

I like the format: dry, informative, good clear illustrations.

Love the Video, I currently am learning some Modern Differential Geometry where Lie-Group Representations are everywhere and I found it hard to appriciate those. Learned to know better today, definitely have a deeper appriciation for those now!

appreciated this video, I too once tried to do an "intro to representation theory" talk as part of the final project for one of my classes and failed. The specific thing I was struggling to understand and still don't fully get is that most proofs that graphs have certain expansion properties (and sometimes how markov chains mix) in theoretical CS involves using representation theory to analyze the eigenvalues of a matrix that is the adjacency matrix of a graph but also somehow related to a group

great content. i like how you are able to simplify such complex subject into something easy to digest.

This is a cool video. You explain things in a way that I can actually understand. Thanks

This is great, I've had a hard time coming to understand group theory, and your video is one of the best I've seen.

wow, that construction with 5 cubes is neat!

Great video! Looking forward to many more

this is an amazing video. "real-time" learning is extremely educational

Absolutely amazing video! Subscribed.

What a cool video! Great work!

This was just right for me. Thanks for the good intro to this subject.

Amazing video, wish I had this when first learning groups for motivation

This is a great video you need to keep doing more please!!!!!!

Although maybe not the most rigorous treatment you maintained my attention and attracted me to a subject that I thought would be a lot more complex than it is, at least the gist of it.

Exceptionally good content , make more please

Thanks for the video man. I saw some comments pointomg out at your mistakes, I just want you to know that it's not that big of a deal for the uneducated public. I personally lack a formal education on this topic (only lineal algebra) and now I feel like I can come to understand it better with self study. This video values clarity over rigor and I'm thankful for that, it's not supposed to be a science article after all.

Actually, this video is wonderful, and I thank you very much for this effort, but I expected more, and I am still waiting for more of your videos, I know that it is very difficult, so thank you

I dropped out from the group theory course just before they introduced representations so it was really enlightening to finally understand what's that all about. xD It's so interesting, this idea of mapping difficult stuff to easier stuff is even quite philosophical... 🤔

Nicely done!

Excellent job!!!

Excellent video! Thank you.

I’d recommend watching Another Roof’s series on Set Theory before this, as I noticed I was constantly thinking about those videos to make sense of the beginning of this one

Splendid! I understood almost everything but the mapping part though

Great video! One small nitpick, at 8:30 I think you made a typo with the matrix multiplication shown at the bottom of the screen. At a_21 I think you meant for it to be 1 not -1 b/c the resulting matrix from what you have yeilds (-2,-5) not the desired (-2,-1).

hi, wonderful video!! what is the font you're using? I love it

Truly excellent.

Great video.

Mind blowing 😮

Wonderful!

Now I want a Megaminx-shaped(Dodecahedron) rubics cube where you can turn only along the internal cubes! But really good video!

That is very nice ..very important..very clear.. Thank you

excellent intro, my compliments. pity that you did not continue further into the topic.

Thanks a lot! It works for me!

Great stuff

This was a brilliant video - super engaging! As an educational video creator myself, I understand how much effort must have been put into this. Liked and subscribed, always enjoy supporting fellow small creators :)

Groups must also have associativity. [(a x b) x c = a x (b x c)] (2:51)

Amazing video

Fantastic!

How can we find the result matrix from the input group?

Great introduction to representations! Indeed, transformations from one mathematical field to another are exremely important. Subscribed!

I hope you make more videos.

Please do more on the fermat thing. 😃

What’s the link between group homomorphisms and topological homeomorphisms? I mean they sound similar, and one professor on yt described homeomorphisms in the same way you described homomorphisms, which is that they allow you to deform a difficult problem into a simpler one, and solve the simple case instead.

Maybe a technical detail you could mention is, that a vector space is more abstract and can be fairly easy defined by a few axioms, or even from the group axioms. And R and C are not the vector space V, they can be the fields over which the scalar multiplication is defined.

14:53 I'm crying "No I will not explain"

"We even teach it to CS students" lol 🤣 Now seriously, nice video. I always found this topic fascinating and I have seen both videos you cited and none was satisfactory enough. Too shallow or to fast into the abyss. Your video had small scope but the right pacing. I would only try to fix the audio for the next one. I'm sure there is a way to filter that high pitch tone. It was a little distracting. Either way, it was a good one. Congrats!

First time in my life I could understand something in maths.

16:35 edit: ohh i just read the comment of Peabrainiac, ok, to exclude overcounting of 0° rotations, and include rotations 180° around edges, 1*{0°}+2*V/2+1*E/2+4*F/2=1+2*20/2+1*30/2+4*12/2=1+20+15+24=60 ok now it's back to being good, point was there was miscalculation unedited: rotations of dodecahedron sequence of 5 rotations around 12 faces, but opposite faces are parallel which means for every 1 rotation there is double counted rotation form parallel face, so 5*12/2=30 but there are unaccounted 30 rotations around vertices, sequence of 3 around 20 vertices with double counting the the opposite, so exactly missing 3*20/2=30 awesome vid so far :D

Bravo 👏

That was basically my linear algebra 1 course))

so the idea of langlands is to have representation of different types of numbers into geometries?

For your next video you might wanna: 1) think about how much each part of the video adds or takes away from the whole, and if it adds, but doesn't add a lot, maybe it's not worth it if it's not integral to the concept 2) use keyframes and the gain setting, or the cutting tool, in a video editor to take out any noises 3) show, don't tell, when you're trying to get a point across glhf

yeahhh, i like this style.

Thank you for the video, I found it very helpful at my level of math self study. Ignore the negative energy from the nit pickers

Is there a typo @ 8:2, the matrix should have 1 not -1 in the bottom left entry or

I thought that all possible groups had been classified. It's one of the biggest pieces of work in mathematics that took over 30 years but it's now complete.

cool good job

the crow break 👌

18:56 "you know we teach matrices to cs students so you know its not that bad" hahaha. cs student here so true and it kinda hurts .

The acting in the beginning was really cute ^v^

post more videos please!!!

5:30 V is not R or C. V is the vector space. So at least R^n or so.

18:49 i feel attacked

Nice

Hi there, is there a way I can contact you personally (for example, a DM on Twitter or an email address)? Great job.

Bird does cool wooo sound. Wooo.

Great video, I learned a lot, but I did find some errors. Some errors: 2:28 - The group definition requires that the operation on the set is associative. 5:45 - A vector space V is not just R or C, in fact, these are usually what vector spaces are over (fields). Every finite-dimensional vector space does indeed have a matrix representation given a certain basis, but V can be infinite-dimensional as well. This is more a technical note, focusing only on GL(R) and GL(C) is totally fine!

I think you have a typo at 8:44, the first column of your basis vectors should be (-1, 1) not (-1, -1)

I did a video on the three identities of zero.

Thumbs up

A group needs closure and associativity too.

the prequel to pascals triangle

👍

Is the bird okay?

Don't know why youtube pushed this video to me, maybe because I watched a bunch of videos on AdS/CFT Duality, which could be a good example of representation.

'seems like its a legit paper... it's in the annals'.... lmao

42

You got 41 k views on your 1st video

feel like everyone knows this shit but its impossible to put it into words

How the youtube know that I am studing representation?

Me-: I finally found a video on KZfaq that explains the FLT proof My mind:_ It's been 20 minutes and there are only 2 minutes left. Me-: I just have to be patient, maybe he will explain the proof in the last two minutes. Video -: And this was what the arrow you see in the proof means hhhhhhhhhhhhh

I think you made a mistake at 5:26. V would be R to the power of the dimension of the vectorspace, i.e. the number of rows and columns of the matrix. So the correct way of saying htat would be that the vectorspace has the ground field R or C.