Summer of Math Exposition

Presented by 3Blue1Brown 3blue1brown

Recurrence and Permutations

Audience:

Tags: combinatorics

The video is a gathering of results from combinatorics that, albeit very useful, are not usually taught at an entry to intermediate level even in a math course.


Analytics

5.41 Overall score*
97 Rank
13 Votes
8 Comments

Comments

6.5

Great video, but I got the impression it’s too algebraic with little intuition presented, and purely algebraic manipulations tend to be hard to follow on the first try. E.g. adding some intuition on why characteristic functions are useful would be nice.

7

I really loved the initial part , but I can’t really understand what’s going on from the characteristic equation part. You start by defining terms and getting into them,but instead you could first state some problems and then could bring those definitions in light based on them, this will give us a great understanding of why there’s such a definition.

3

Your explanations were clear and the cat is very cute! You picked a topic that hasn’t been covered too much by math videos in the past, but I think there’s a good reason for that. Generating functions are notoriously abstract and without visual intuition. Recurrence relations can be visually pleasing but you chose to cover them as a textbook would. So your video is mostly long sequences of equations and definitions, which is pretty hard to stick with for almost 40 minutes. I would also try to work on your animation style to make it more unique. I understand it’s hard when using manim (I use it too), but some good first steps include changing the background color, using a custom color palette, avoiding the Write animation, and changing the font. I also would avoid the Transform animation, not just because its unoriginal, but because it can be visually confusing. It’s implementation is rather naive so the matching symbols don’t always line up. Lastly, try arrange your scenes in a more interesting way. I understand the urge to arrange everything vertically down the middle of the screen, but it gets very repetitive.

I know this hasn’t exactly been a gushing review, but I hope you do continue making things. You’re clearly a very good expositor and, with a better choice of topic and greater attention to animation, I think you can make some really great content.

5.4

A solid video.

I really like this topic, and there were a lot of nice moments in the video. For example, I loved the Fibonacci section and the graph because it added more insight to the topic that a student might not get from their textbook. I also liked the application at the end.

My main issue was the pacing felt a bit unpredictable for me. In some cases it was too slow - some of the addendums and examples took away from the overall clarity because they wandered from the point. Then other moments like the characteristic equation segment felt rushed.

I also felt the animations in some instances didn’t help with the clarity - for example, I didn’t feel the bracket segment was explained in a particularly intuitive way. Maybe the animation could have highlighted which brackets you were talking about?

This could have been better as a series of videos perhaps.

6.2

I think you tried to cover too much with a single video. I would recommend focusing on just one recurrence, for example just covering the recurrence that generates the Fibonnaci sequence or just the one that generates the Catalan numbers. I am saying this because if I hadn’t watched this video as a SoME4 entry, I wouldnt’t have finished it probably because of its lenght.

Around minute 5, the were some problems with the animations for the branches of the tree. Using “FadeIn” instead of “Transform” might have worked better, since branches are simply being added at each step.

Despite these suggestions, I am glad I watched your video because I learned about methods for recurrence relations I wasn’t familiar with, and I found them very interesting. Thank you for your work!

6.6

It took 3 minutes to introduce a question that hooks the listener. I think it would improve the engagement to start with the tree question and sample before introducing vocab about recurrence.

All the pieces are there for a good piece, but could be reordered for more student engagement.

Additionally, this may have been better to split into multiple videos in a series to not overload a student

4

The first half of the video had a lot of text on the screen without much visually adding to the explanations. The second half of the video was better in this respect.

6.2

Strong mathematics and clean animations throughout. I definitely learned some interesting things about recurrence relationships in unexpected contexts—the parenthetical sequences were quite cool!

My biggest piece of advice is to show rather than tell (or perhaps show alongside telling). As this type of mathematics can be somewhat overwhelming/easy to lose track of when presented in written form, it would be excellent to lead with intuitive visualizations and analogies to the real world, so the viewer gains intuition. A few concrete examples might include:

  1. For the tree problem, the wording was a bit confusing/hard to visualize, especially around which branches could make new branches. I would consider starting by presenting the visualization of the growing tree while discussing the rules alongside it, which would be much easier for viewers to understand quickly. I would also make the connection to Fibonacci much sooner, as it would help grab the viewer’s attention and connect something they might not have explicitly heard of (recurrence relationships) to something they’ve almost certainly heard of through “math pop culture” (Fibonacci numbers).

  2. Additionally, when discussing growth rates of various sequences, it would be amazing to actually see the recurrence operation applied to something visual/physical—perhaps a group of squares/units at each step so we can see how quickly we end up with lots of them!

  3. In the last bit on permutations and stochastic paths to a point, I would love to see the full grid of paths drawn so you could connect it to canonical maze/orthogonal street problems—a great real-world analogy would be to ask how many ways there are to walk from one intersection to another in Manhattan! This could help motivate the question with something very tangible, which would ease the transition into the parenthetical problem (which I found trickier to connect to the stochastic paths).

For people with a strong background in lecture-based mathematics, the written equations are likely sufficient for understanding, and they’re well presented. But with a few pedagogical changes, prioritizing “showing intuition” before “telling math” I think this could reach a very broad audience and leave viewers with a more lasting impression.