Mu Prime Math
2: Repeated Roots - Dissecting Differential Equations
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Paper on real induction: arxiv.org/pdf/1208.0973
Proof by induction is often taught as something that only works for integers, natural numbers, or whole numbers. However, there's an analogous concept to induction that applies to intervals on the real numbers, even though the real numbers are an uncountable set! This video explains and proves the result for the interval [0,1], which can be generalized to arbitrary closed intervals in the real numbers.
Topology playlist: youtube.com/playlist?list=PLug5ZIRrShJEGnUPxM1KUVOHkW4kN6QU_
0:00 The Theorem
4:36 Proof
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Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
0:00 The Derivative
2:14 The Square
7:50 Generalization: Cauchy Products
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Original based on Grossman & Turett: arxiv.org/pdf/math/0606253
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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Did you know about this very nice equation with the matrix exponential? In this video we prove the result by reducing to the upper triangular case and connect it to basic identities of the exponential function.
Learning Linear Algebra playlist: youtube.com/playlist?list=PLug5ZIRrShJHNCfEiX6l5CKbljWayGEcs
0:00 Reducing to Upper Triangular
8:53 Main Proof
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Learning Linear Algebra playlist: youtube.com/playlist?list=PLug5ZIRrShJHNCfEiX6l5CKbljWayGEcs
0:00 Upper Triangular Definition
1:25 Product is Upper Triangular
6:42 Diagonal Entries
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Robert J. MacG. Dawson. “On a “Singular” Integration Technique of Poisson”. American Mathematical Monthly, 2005. cs.smu.ca/~dawson/Poisson.pdf
We can compute the integral of e^(-x^2) using a very cool trick that lets us switch to polar coordinates and use the Jacobian for a u-sub. But does this technique work for any other function? In this video we turn that problem into a differential equation and find all of the solutions!
Mariano Suarez-Alvarez's proof: math.stackexchange.com/a/4517530/713547
0:00 The Functional Equation
4:23 The Differential Equation
7:14 Solving
12:34 Additional Notes
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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This video proves the uniqueness of the tensor product of vector spaces (or modules over a commutative ring). This uses the universal property of the tensor product to prove the existence of an isomorphism (linear bijection) between any two "tensor products".
Tensor Products playlist: youtube.com/playlist?list=PLug5ZIRrShJHCtzgzZyRqSdzr8wYlN2qk
0:00 The Universal Property
3:53 Relating Two Tensor Products
8:10 Proving Isomorphism
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Generating set proof: youtu.be/KnSZBjnd_74?t=1437 timestamp 23:57
If we have a basis for each of two vector spaces (or modules over a commutative ring) V and W, then we can use that to form a basis for the tensor product V⊗W. The proof uses the universal property of the tensor product, which connects bilinear maps on the Cartesian product to linear maps on the tensor product. This video explains how we can use the universal property to prove the tensor product basis. The goal is to improve our understanding of the applications of the universal property.
Tensor Products playlist: youtube.com/playlist?list=PLug5ZIRrShJHCtzgzZyRqSdzr8wYlN2qk
0:00 Introduction
1:43 How to Prove Linear Independence
6:18 Using the Universal Property
12:11 Conclusion
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The universal property of the tensor product is one of the most important tools for handling tensor products. It gives us a way to define functions on the tensor product using bilinear maps. However, the statement of the universal property can be confusing if it is presented without background. This video is an explanation of the universal property that proves it for a concrete instantiation of the tensor product of vector spaces (or modules over a commutative ring).
Tensor Products playlist: youtube.com/playlist?list=PLug5ZIRrShJHCtzgzZyRqSdzr8wYlN2qk
0:00 Introduction
3:04 Constructing the Tensor Product
7:54 Bilinear Maps
10:39 Maps on the Tensor Product
16:17 Defining g
26:24 Linearity and Uniqueness
29:44 Universal Property
30:50 Example
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0:00 Problem Introduction
5:42 Solution
10:34 Non-example: Integers mod 5
11:13 Example: Alternating Group
Group Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJHDvvls4OtoBHi6cNnTZ6a6
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Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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Group theory playlist: youtube.com/playlist?list=PLug5ZIRrShJHDvvls4OtoBHi6cNnTZ6a6
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0:00 Setup
6:18 Homomorphism
8:50 Injective
10:35 Surjective
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More details on why the integral is the inverse of e^x:
We proved in the video that any right inverse to e^x must equal that integral. However, we didn't prove that e^x has a right inverse in the first place.
We know that e^x : R → R+ is a strictly increasing function whose output can be made arbitrarily large or arbitrarily small. Therefore e^x is a bijection R → R+. Every bijective function has a two-sided inverse (see [1] below). Therefore e^x has a two-sided inverse, which in particular is a right inverse. I proved in video [2] that injective functions have at most one right inverse. Therefore the right inverse to e^x is unique if it exists. But we already know that there exists one right inverse that is also a two-sided inverse. We conclude that there exists exactly one right inverse to e^x and that this right inverse is also a two-sided inverse. Hence the integral in the video is a two-sided inverse to e^x.
[1] youtu.be/E-njuKKrOwg
[2]: youtu.be/i5ZJuJr8DwE
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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Topology playlist: youtube.com/playlist?list=PLug5ZIRrShJEGnUPxM1KUVOHkW4kN6QU_
Timestamps:
0:00 connectedness
9:59 path-connectedness
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The sum of all natural numbers, and the sums of divergent series more generally, are often debated because it seems incoherent to say that a divergent sum equals a finite number. This video explains the machinery used to obtain finite outputs from divergent infinite series.
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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Learning Linear Algebra playlist: youtube.com/playlist?list=PLug5ZIRrShJHNCfEiX6l5CKbljWayGEcs
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Challenge Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGkzGsXMYQt8bi5ImYtiEMM
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Proofs that use the delta-epsilon definition of the limit can be confusing because it seems like we can prove that the limit is anything we want if we pick the right value of delta. In this video we prove that limits are unique and go over some examples of disproving limits!
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
0:00 Background
3:46 Example 1
9:46 Example 2
15:45 Backward proof?
17:14 Proof of uniqueness
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Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
0:00 Why the sum diverges
7:33 Why grouping fails
12:57 When grouping is valid
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Bringing functions outside of a limit is very useful for calculating limits. But when does this rule work? This video gives a proof and explanation of why we can switch limit and function if the outside function is continuous and the inner limit exists.
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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Topology playlist: youtube.com/playlist?list=PLug5ZIRrShJEGnUPxM1KUVOHkW4kN6QU_
0:00 Intro
1:24 Closure
7:46 Boundary
11:05 Interior
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Functions playlist: youtube.com/playlist?list=PLug5ZIRrShJG35bSmijiKFxerMar8jMCi
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Functions playlist: youtube.com/playlist?list=PLug5ZIRrShJG35bSmijiKFxerMar8jMCi
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Functions playlist: youtube.com/playlist?list=PLug5ZIRrShJG35bSmijiKFxerMar8jMCi
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Challenge Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGkzGsXMYQt8bi5ImYtiEMM
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Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
0:00 Orthonormal
10:19 Basis
21:15 Summary
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Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
In this video, we use F[x]-modules to prove that a matrix is invertible if and only if its determinant is nonzero. Another example of how F[x]-modules can be applied to a ton of things in linear algebra!
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Group Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJHDvvls4OtoBHi6cNnTZ6a6
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Learning Linear Algebra playlist: youtube.com/playlist?list=PLug5ZIRrShJHNCfEiX6l5CKbljWayGEcs
Tensor Products playlist: youtube.com/playlist?list=PLug5ZIRrShJHCtzgzZyRqSdzr8wYlN2qk
0:00 Construction
14:01 Examples
23:33 Basis for Tensor Product
28:44 Examples
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Euler's formula for the complex exponential can be proved in many different ways, such as with Taylor series. Here we find Euler's identity using a limit equation for e^x and the polar form of complex numbers!
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
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Challenge Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGkzGsXMYQt8bi5ImYtiEMM
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Characteristic polynomial explanation: youtu.be/jCt6mR3QtPk
Intro to F[x]-modules: youtu.be/H44q_Urmts0
The Cayley-Hamilton theorem says that every matrix is a root of its own characteristic polynomial, det(xI-A). With all of our knowledge of F[x]-modules, the proof is simple! This video is an explanation of how we reach this important result in linear algebra.
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
0:00 Proof
6:32 Example
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Similar matrices isomorphism: youtu.be/-ligAAxFM8Y
Intro to F[x]-modules: youtu.be/H44q_Urmts0
The characteristic polynomial described by the determinant det(xI-A) is very useful when studying matrices. It turns out that it's related to modules as well! Here we show how the characteristic polynomial is related to the module form of an arbitrary matrix.
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
0:00 Computing the determinant
10:07 Similar matrices have same polynomial
12:40 Proof for a general matrix
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Every module is a direct sum of cyclic modules: youtu.be/gWIRI43h0ic
Intro to F[x]-modules: youtu.be/H44q_Urmts0
The rational canonical form and Jordan normal form of a matrix are very important tools in linear algebra, but ring theory and module theory give us a very effective way to prove their existence! Here we show that every matrix is similar to a matrix in rational and Jordan canonical form.
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
0:00 Rational canonical form
14:17 Every matrix is similar to RCF
18:33 Algebraically closed fields
20:10 Jordan canonical form
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Modules over a polynomial ring are powerful tools to study linear algebra. This video is an explanation of why similar matrices are related to isomorphisms of F[x]-modules!
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
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Music: OcularNebula - The Lopez
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
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Learning Linear Algebra playlist: youtube.com/playlist?list=PLug5ZIRrShJHNCfEiX6l5CKbljWayGEcs
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Splitting explanation: youtu.be/ZINtBNje_08
In this video we give a proof of the classification theorem using two smaller proofs by induction. We show both the elementary divisor form and the invariant factor form of a module. This theorem tells us a lot about modules over a principal ideal domain!
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
0:00 First lemma
2:15 First lemma proof
8:51 Second lemma
9:24 Second lemma proof
11:20 Proof for p^r
28:30 Final proof
36:35 End of proof (additional explanation)
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Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
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Music: C418 - Pr Department
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
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Music: C418 - Pr Department
Ring & Module Theory playlist: youtube.com/playlist?list=PLug5ZIRrShJExMapwnaKTFXDYbKeWDXq7
0:00 Prime ideal
3:06 Maximal ideal
9:16 Maximal implies prime
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Relativity of simultaneity can be very confusing the first time you see it because it doesn't match everyday experience. However, it turns out that we need simultaneity to be relative for physics to work! Here we use linear algebra to explain why events that are simultaneous in one reference frame are not simultaneous in another reference frame.
Special Relativity playlist: youtube.com/playlist?list=PLug5ZIRrShJHWM8_CPL5Nh5mPlEUNor0q
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Special relativity gives us a lot of unintuitive results. We can understand why these happen using the Lorentz transformation, so we can see how coordinates in one inertial reference frame appear to an observer in a different reference frame!
Special Relativity playlist: youtube.com/playlist?list=PLug5ZIRrShJHWM8_CPL5Nh5mPlEUNor0q
0:00 Length contraction
5:44 Relativity of simultaneity
10:08 Time dilation
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The spacetime interval s^2 = ct^2 - x^2 is important in special relativity because it stays the same in all inertial reference frames. Here we use some linear algebra to give a proof of exactly why this interval is invariant!
Special Relativity playlist: youtube.com/playlist?list=PLug5ZIRrShJHWM8_CPL5Nh5mPlEUNor0q
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Why the eigenvalues need to be positive:
We can write the vector (β,1) as a linear combination of the two eigenvectors. If one of the eigenvalues is negative, then (β,1) will get flipped along one of the axes of the eigenvectors. Because |β| is less than 1 we know that (β,1) starts out in the top region, above y=x and y=-x. Once it gets flipped it won't be in the top region anymore. In that case, it can't possibly equal (0,1) because (0,1) is in the top region. This contradicts our assumption. Therefore the eigenvalues can't be negative because that leads to a contradiction.
The eigenvalues also can't be zero because then there would be a nonzero null space, so the map would not be injective (multiple values map to zero), so it would not have an inverse. As a result, we know that the eigenvalues must be positive.
The Lorentz transformation is often derived using thought experiments about shooting light rays and things like that. But we can prove the matrix form of the Lorentz transformation in a more abstract way using linear algebra! This gives us a way to describe changes of coordinate system when we move between inertial reference frames.
Special relativity playlist: youtube.com/playlist?list=PLug5ZIRrShJHWM8_CPL5Nh5mPlEUNor0q
0:00 Starting assumptions
6:20 Derivation
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Dr Peyam video on f(x+y)=f(x)+f(y): youtu.be/WnglFnfjjFs
Special relativity intro: youtu.be/upfIW5Ci0mQ
One of the most important starting points for deriving the Lorentz transformation is the fact that it is a linear transformation. Why do we get to assume that? Here we explain the intuition behind why we expect the Lorentz transformation to be linear, using the coordinate systems of special relativity and how rulers and clocks change between inertial reference frames.
Special Relativity playlist: youtube.com/playlist?list=PLug5ZIRrShJHWM8_CPL5Nh5mPlEUNor0q
0:00 Introduction
4:48 T(u+v) = T(u)+T(v)
15:13 T(cv) = cT(v)
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Special Relativity playlist: youtube.com/playlist?list=PLug5ZIRrShJHWM8_CPL5Nh5mPlEUNor0q
0:00 Reference frames
5:19 Spacetime diagrams
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When is the derivative of area equal to the perimeter? In this video we solve this calculus/geometry problem for any shape. Then we look at regular polygons and get some very interesting results!
Calculus Problems playlist: youtube.com/playlist?list=PLug5ZIRrShJGFne7YhMi-4eYsUKzkITao
0:00 General case
6:21 Examples
9:26 Regular polygon case
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