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Andrew McCrady
เข้าร่วมเมื่อ 14 พ.ย. 2011
Here you'll find videos about a variety of math subjects that are aimed at helping undergraduates, graduate students, and math enthusiasts alike.
Reacting to my Fall 2024 Course Evaluations
Let's take a look at student feedback in my Fall 2024 courses.
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The Primitive Element Situation is Crazy
มุมมอง 23K14 วันที่ผ่านมา
The Primitive Element Theorem was a big advancement in field theory. But what does it even mean? I'll explain what a field is, some interesting math history for context, and how to use Sage to easily do some BRUTAL algebra.
How You Should Think About Infinite Cartesian Products
มุมมอง 925หลายเดือนก่อน
I regularly teach a topology class online, and often it's the first time my students encounter infinite Cartesian products of sets. This video aims to help you understand what elements of such products look like. Thank you for supporting my channel!
Kepler's Second Law as Understood by a Mathematician
มุมมอง 4045 หลายเดือนก่อน
Kepler's 2nd Law is one of my favorite applications of calculus and vectors. I only took one physics class during my school career, so my physical intuition isn't always great. But this proof relies mostly on math, and showcases how mathematics is a language to describe all that's around us (some physics stuff, anyway). I found the proof that I cover here in Krantz's textbook "Differential Equa...
The Subgroup Tests in Under 3 Minutes! Fast Abstract Algebra Help
มุมมอง 917 หลายเดือนก่อน
How do you show a subset of a group is a subgroup? Do you have to check all the group axioms? We'll talk about two ways to test if a subset of a group is a subgroup, and demonstrate how to do the tests with two examples. Hopefully this makes you feel better prepared to solve these kinds of group theory problems!
A Precursor to Group Theory
มุมมอง 6447 หลายเดือนก่อน
Here's a fast but clear introduction to group theory, which makes up a substantial part of a typical abstract/modern algebra class. Before you get frustrated with a super abstract textbook, take 10ish minutes understand the key concepts of group theory with examples and simple explanations. Please like and subscribe to help grow the channel!
Partial Sum Formulas and Asymptotic Analysis
มุมมอง 2417 หลายเดือนก่อน
Finding a summation formula to add the first n natural numbers is easy. Finding a summation formula to add the first n reciprocals is impossible, literally. At least in terms of elementary functions. This video dives into asymptotic analysis to prove there's no "nice" formula for the harmonic numbers. It's a great application of freshman calculus, how long can you follow along? Thanks to a view...
Homotopy Classes, the Path Product, and Associativity
มุมมอง 3559 หลายเดือนก่อน
We give clear explanations visuals for the path product and homotopies of paths in a topological space. We focus on the fact that the path product is not necessarily associative, but that we can extend the path product to equivalence classes of homotopic paths, and show that the path product is associative on these homotopy classes. Along the way we show that a path is homotopic to any reparame...
Homotopy Intro
มุมมอง 4229 หลายเดือนก่อน
Homotopy between paths in a topological space can be tough to understand. This video aims to make it easy to understand! We'll intuitively define what a homotopy between paths is, use pictures and demonstrations to understand this idea, then use this to understand the rigorous definition of a homotopy, along with examples. This video is part of a growing playlist of mine dedicated to topology. ...
Paths and the Path Product
มุมมอง 2129 หลายเดือนก่อน
This topology video introduces paths in a topological space, and then the path product. This is the first video introducing some material needed to discuss the homotopy groups of a topological space. We carefully go over the definitions and animate some examples. The only prerequisite is knowing what a topological space is. I'm aiming to make this an easy introduction to algebraic topology.
ElGamal Encryption and Elliptic Curve Cryptography
มุมมอง 29510 หลายเดือนก่อน
This video explains and illustrates all aspects of ElGamal Encryption and Elliptic Curve Cryptography through the story of Alice and Bob. Will Alice's secret message make it to Bob? More information about elliptic curves and elliptic curve cryptography: www.ams.org/journals/mcom/1987-48-177/S0025-5718-1987-0866109-5/S0025-5718-1987-0866109-5.pdf th-cam.com/video/RtiVaALdqX0/w-d-xo.html wstein.o...
Why is the orbit of a planet in a plane?
มุมมอง 1.1K11 หลายเดือนก่อน
Why is the orbit of a planet in a plane?
Visual Calculus: Fubini's Theorem for Iterated Double Integrals
มุมมอง 655ปีที่แล้ว
Visual Calculus: Fubini's Theorem for Iterated Double Integrals
The Alexander Subbase Theorem: help understanding the definitions and the proof
มุมมอง 745ปีที่แล้ว
The Alexander Subbase Theorem: help understanding the definitions and the proof
Understand The Baire Category Theorem: Dense Sets, Nowhere Dense Sets, & Infinity
มุมมอง 3.1Kปีที่แล้ว
Understand The Baire Category Theorem: Dense Sets, Nowhere Dense Sets, & Infinity
Piecewise Continuous Linear Functions are Dense Among Continuous Functions
มุมมอง 842ปีที่แล้ว
Piecewise Continuous Linear Functions are Dense Among Continuous Functions
The Axiom of Choice: History, Intuition, and Conflict
มุมมอง 10Kปีที่แล้ว
The Axiom of Choice: History, Intuition, and Conflict
Cards, Marriage, and Python: an Introduction to Graph Theory
มุมมอง 243ปีที่แล้ว
Cards, Marriage, and Python: an Introduction to Graph Theory
Can you solve these three tricky counting problems?
มุมมอง 101ปีที่แล้ว
Can you solve these three tricky counting problems?
How many squares are on a chessboard? And more!
มุมมอง 351ปีที่แล้ว
How many squares are on a chessboard? And more!
How many triangles are there in an n by n grid?
มุมมอง 564ปีที่แล้ว
How many triangles are there in an n by n grid?
The Complex Logarithm: Multivalued Functions?!?
มุมมอง 1.4Kปีที่แล้ว
The Complex Logarithm: Multivalued Functions?!?
How Harmonic Functions Relate to Holomorphic Functions
มุมมอง 753ปีที่แล้ว
How Harmonic Functions Relate to Holomorphic Functions
The Extended Complex Plane (Riemann Sphere)
มุมมอง 5K2 ปีที่แล้ว
The Extended Complex Plane (Riemann Sphere)
The Stereographic Projection: Learn it FAST!
มุมมอง 11K2 ปีที่แล้ว
The Stereographic Projection: Learn it FAST!
It is crazy
you are so under-rated!!! Your content is a gold mine for number theory in math olympiads!! You've got a new subscriber!! :)
Thank you for your comment!
Very cool video! I had never seen these concepts before. Also never seen Sage. In the past I would use an ancient piece of software called Maxima to do algebra, whenever I got bored of doing it by hand. It seems Sage is a newer Python-based alternative, but it looks like they haven't figured out graphical input and output of mathematical formulas yet? One question: is (³√2 + ³√3) just one example of a primitive element for the field ℚ(³√2, ³√3)? I suppose any number of the form (a ³√2 + b ³√3 + c) with a, b, c ∈ ℚ would be a suitable alternative. But do all of its possible primitive elements have this form? Also, what happens when you keep adding all possible roots to ℚ? Since both the root arguments (ℕ) and the root indices (ℕ) are countably infinite, all possible roots are also countably infinite, by a similar diagonal construction as for ℚ. (Does the set of all possible roots have a name?) So the resulting extension would be isomorphic to a countably-infinite vector space of ℚ... which sounds a lot like ℝ. Is this yet another construction or definition of ℝ? Do transcendental numbers naturally appear in it, even though they were not included in its construction? Also, the primitive element theorem clearly does not apply, because it's not a finite extension, but what would a degenerate primitive element of this infinite extension look like? The... sum of all possible roots?
Thanks for watching! I’m not familiar with Maxima. Sage can do some plotting pretty similar to what you can with matplotlib in python. Yes this is just one example of a primitive root, there in fact many different combinations that could work. Here’s the proof sites.math.washington.edu//~greenber/MATH404-PrimElem.pdf You won’t quite get the reals from a process from this, since transcendentals aren roots of polynomials. You get a number field called the “algebraic numbers”.
Please keep clickbaiting math! 🎉
Do complex integrals and the residue theorem please
This is awesome, especially the Sage Math demo. This is the type of thing that should have been given as hw in my abstract algebra II class where Sage Math could be used instead of keeping the problems computationally simple enough to do on paper, which forces the set of available hw problems to be quite boring.
Thank you for the comment! I look forward to exploring more of what neat abstract algebra stuff that Sage can do.
Great 👍
Thank you, I hope it was helpful!
you should have made your first basis vector gamma^0 = 1 and not used gamma^9, but the linear combinations that make alpha and beta didn't end up using the gamma^9, so I don't have that much of an issue.
Thank you for the comment.
Seems like an interesting video, but so quiet that it's actually hard to watch lol
Yeah I plan to try a different volume setting on the next vid. Thanks for watching!
The short form content is great, enough to intrigue and a great sell to watch the full video. Gonna have to check it out, please keep sharing!
Thank you for watching!
You successfully tricked me into reviewing my abstract algebra knowledge
Thank you for watching!
Amazing video! What software did you use to animate it?
Thank you! Trying to get better at Manim like 3B1B.
@@DrMcCradythank you for sharing!! This is some amazing math history!
Title should’ve ended with ellipsis
Thank you, the next one will.
Phrasing an abstract algebra explainer as if it's youtube drama is quite possibly the greatest thing I've ever seen. You could teach so much to unsuspecting high-schoolers by making titles like this hahaha
no need just see the equation , it say it all.
I think the issue is that equations don’t necessarily speak to everyone, or that some people need more information or a different medium for understanding concepts.
En los últimos días, he estado ocupado tratando de construir la raíz cúbica de tres en el plano. Claro, demostré que es imposible. Y luego, aparece este video recomendado, fruto de cómo me espía el algoritmo
That is creepy, but I am hopeful my video was interesting. Thank you for your comment.
How is it possible that this channel does not have 250 000 subscribers?
Amirite?? Thank you!
Elementary, my dear Watson!
Great video, and the history at tme beginning helped to explain the motivation for studying these field extensions. (I've only taken a basic Abstract Algebra class that never reached the topic of field extensions.) And, yes, like everyone else is saying, I clicked for the silly title too, haha!
I didn’t really get into the history in undergrad. I feel like it’s hard to do since it requires a LOT of context and familiarity with some advanced concepts.
Pretty random but I watched your Topology playlist for a whole semester, did so good in my class that my professor offered me an undergrad research opportunity :) I think I'll owe you my degree when I graduate lol
That’s great to hear! I’m so pleased you found them helpful!
This Is The Greatest Mathematics Of All Time
I will not argue with you.
Thank you kind sir! Never heard of this theorem, nevertheless loved everything about this video: historical bit, explanation, visualisations ❤
Thank you for your comment!
three completely horrible video titles today. it's really wearing me down
Sorry friend, hope your day gets better.
Sorry friend, hope your day gets better..
Great video, I took an abstract algebra class as a comp sci major, and loved learning more about this type of thing. Keep it up!
Thank you!
moistcritical physics
Definitely the inspiration for the title. I Just started getting into his channel this year.
I thought the title meant too many primitive elements are being discovered or sth🤣
Oh my god you mentioned Brahmagupta! Finally professors have stopped teaching that the Greeks and Persians came up with everything! Mathematics has had such a rich history and india was a big part of it, its so sad that this history has been almost totally omitted up until relatively recently. Lots of love, Gaurahari Das
very deep result. Galois couldn't demonstrate it.
It’s interesting that he knew some extent of it.
Here's a fun problem. Let a,b,c be formal variables. Let L be the field Q(a,b,c), and let K be the field Q(a+b+c,ab+bc+ca,abc). Clearly K is a subset of L. (In fact it is precisely the set of _symmetric_ rational functions in a,b,c.) The problem is to prove that L=K(a-b). Note that this is an instance of the primitive root theorem, in the sense that the theorem guarantees us that L=K(gamma) for _some_ gamma in L.
That does sound cool!
You are talking too fast. I can't follow at that speed.
Playback speed -> 0.5 speed 😁
Thanks! You math Guys are great!
Thank you for your comment!
2:30 It is del Ferro, not 'Farro'
But really good video, very well explained
Thank you!
the proof is what's crazy (imo), because it turns out almost all gamma = alpha+x*beta can do the job. But I don't remember if there is some clever choice of x that will always work.
Oh yeah I agree. I’d been watching a lot of Penguinz0 and thought I’d try one of his titles 😁
this is a fun video idea! edit: im also a big fan of judson's free algebra book!
It’s a solid book! We used to teach out of Hungerford’s book, also pretty thorough, but kind of expensive.
the clickbait worked 😂
I can’t believe it either, but I’m happy about it.
Very nice video!
Thank you!
Super cool video! Seeing (gamma = alpha + beta) at the end was a bit jarring though: I think a common reaction to this result would inspire the question "is that just always true?". A quick statement like "in this case, it happens to be..." would help contextualize that answer since the result is presented almost as trivial without explanation. @MasterHigure has a nice comment below that added some important information to this point, though I cannot understand the notation 🙂
Yeah the proof of the theorem shows almost all expressions alpha+t*beta work, but I didn’t want to get into that in the video, rather just demonstrate a particular element works.
I think in Zorn's Lemma we need to specify that there should be an upper bound IN THE SET S, so that the statement holds. Otherwise, we can take the set [0, 1), which doesn't have a maximal element
Yes you’re right, that’s what I was going for but maybe didn’t say explicitly?
You are such a nerd.
Online tough guy
Liked for AD
commenting for the algorithm gods
Thank you for your support as I stand at their altar awaiting judgement.
very good demonstration 👍🏻 really looking forward to more videos from you.
Thank you!
The clickbait situation is crazy, but awesome video 👍🏻
Thank you!
Pi is equal to 3
You’re so close!
Good video. I had no audio issues (saying that because i see other people saying the video is quiet. Listening with headphones, have the volume 3/4 of max and can hear quite clearly.)
Thank you!
Coomer 😂
5:55 You don't need to check whether powers with natutal exponents give new elements. Just the basic multiplication table from a few seconds earlier and a *very* short induction argument. The reciprocals are there because this is a field, after all (if you're being pedantic you have to show that this field exists at all first), and then a very similar induction covers the rest of the negative integer exponents. Completely unrelated: It is very often the case that K(a, b)=K(a+b), but not always. It is the case whenever [K(a,b):K]=[K(a):K][K(b):K]. And the simplest counterexample I've seen (that's not trivial, like K(a-b, b) != K(a-b+b)) is an extension of K(s, t) with K having order p for some odd prime p, and s, t being transcendental. If a is a root of x^(p-1)-s and b is a root of x^p-sx-t, then K(a, b) has degree p(p-1) but K(a+b) only has degree p, as it is a root of x^p-sx-t. K(a, b) is still simple, but a+b isn't a generator.
Sounds very efficient, thank you.
Related to the unrelated remark: If L|K is any finite field extension of degree d, let's say with K-linear basis x_1,...,x_d, then an element u=a_1x_1+...a_dx_d is primitive for L if and only if 1,u,...,u^{d-1} are linearly independent. But this is the same as saying that their coefficient vectors wrt x_1,...,x_d are linearly independent, i.e. that the matrix formed by them has nonzero determinant. But now, this determinant is just a (degree d*(d-1)) polynomial in the variables a_1,...,a_d. Now, from analysis/algebraic geometry, we know that this polynomial is either identical to zero (which means that no primitive element exists) or the set of roots is "small" (a zero set). This second case however implies that "most" elements in the field extension are actually primitive (but writing down such a random element would require all powers, so it is probably not very efficient)
I have a math major and I was lost within 75 seconds :( what is Q? What is Q(i)? Heck I don't remember if R stands for "reals" or something else! Maybe I'm not your target audience :(
ℝ is the real numbers, ℚ the rationals, ℂ the complex numbers, and ℚ(i) (for example) consists of the rational numbers adjoint with i, so you just add i to the rational numbers, and make it closed under addition. This is now a new field.
Oh no! You got R right as the reals! I can see how abstract algebra could be a forgettable topic, and how the symbols could be vague if you haven’t seen them or it’s a been a while. Thank you for your comment.
Great video :)
Thank you!
the stupid title was why i clicked on it btw, good vid
Welcome aboard, thank you!