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An Intuitive Guide to Linear Algebra (2012)

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Re: An Intuitive Guide to Linear Algebra (2012)

#41

I... I still really struggle with this. I'm a smart person, I've got a bachelors of engineering, I've been a professional software developer for around 14 years now, and I've built a house. But there is something about degree-level maths and beyond that I find deeply unintuitive in a way that software development isn't. Through comments here I found 3blue1brown's (clearly much loved) videos. By the third video I was…

Try Gilbert Strang's course at MIT, it's publicly available in video format, and starts from basic principles.

Re: An Intuitive Guide to Linear Algebra (2012)

#42

I... I still really struggle with this. I'm a smart person, I've got a bachelors of engineering, I've been a professional software developer for around 14 years now, and I've built a house. But there is something about degree-level maths and beyond that I find deeply unintuitive in a way that software development isn't. Through comments here I found 3blue1brown's (clearly much loved) videos. By the third video I was…

The problem with Linear Algebra specifically, is that it can be viewed from many different perspectives.

The article here focuses on an "operational" perspective, how the numbers get added or multiplied together to turn into other numbers. However, Linear Algebra is also useful in geometry, and other situations.

This "intuitive guide" to linear algebra sets you up very nicely for figuring out how to add and multiply matricies together. But it doesn't give you any intuition about a rotation (aka quaternions) in 3d space, for example. A lot of math books make the mistake of trying to teach all the perspectives at the same time, instead of focusing on just one viewpoint until the student gains mastery.

A Quaternion is "just" a 4x4 matrix that represents rotation in 3-dimension space. Because you only move 3-ways rotationally (yaw, pitch, and roll), you're "underconstrained" with regards to the 4x4 matrix. Etc. etc. A lot of geometry intuition needs to be built here to really understand Quaternion... and none of that geometry is explored in the blogpost.

Which is fine. Focus is good. But when people approach Linear Algebra, its important to know that its "so useful" that there are too many ways of looking at Linear Algebra... too many different, yet equivalent, understandings of the subject.

Re: An Intuitive Guide to Linear Algebra (2012)

#43
post #11
post #5

Earlier quoted context omitted.

How much of this explainer however seems better to us precisely because of the more comprehensive knowledge and understanding we already have? For example the author uses the word function liberally in the explanation. However, when studying functions in school in math it was super complicated for me. It was only after I started programming, learning the programming language meaning of function, and then when I was r…

As someone who learned to program before taking any interesting math I was always so confused by the amount of early math classes spent explaining function notation. It wasn't until I tried teaching people that I realized how odd the notation can seem.

you should be happy someone explained it to you- I feel that notation was overlooked tremendously in my math education- I actually just brought this up in a thread yesterday. It was like "oh, we have this dx now... k."

Re: An Intuitive Guide to Linear Algebra (2012)

#44

While this explanation is certainly much clearer than what I remember of high school maths, I still have a pretty tough time following the formula examples. When I see A(x) = ax, I'm not entirely sure how to read it. Is A meant to be a function that accepts x? If so, why is the equivalent expression a * x? Is it supposed to be implied that function A also has some hidden value "a" that is going to be multiplied by th…

I agree that this was a bit confusing. Higher up in the article, it shows that a linear function is one that doesn't change when scaled:

F(a * x) = a * F(x)

This is showing the relationship between two uses of the same function.

Then, further along, we find:

"So, what types of functions are actually linear? Plain-old scaling by a constant, or functions that look like: F(x)=ax In our roof example, a=1/3"

I think in this second situation, F(x)=ax is not a relationship but rather a DEFINITION of the function F(x).

In programming terms:

function F(x: real) : real;

begin

  Result := x * (1/3);
end;

Re: An Intuitive Guide to Linear Algebra (2012)

#45

I... I still really struggle with this. I'm a smart person, I've got a bachelors of engineering, I've been a professional software developer for around 14 years now, and I've built a house. But there is something about degree-level maths and beyond that I find deeply unintuitive in a way that software development isn't. Through comments here I found 3blue1brown's (clearly much loved) videos. By the third video I was…

This is typical for many people. You love pre-college math because you have intuitive understanding, while college-level maths offer a new level of abstraction that you may not feel familiar with from the get-go.

It's perfectly okay not to learn linear algebra, by the way, especially when you don't find any incentive to do so. Otherwise, you'll find linear algebra to be one of the most intuitive tools to model so many problems.

If you do want to learn linear algebra or any other higher math, I'd strongly recommend you focus on understanding concepts intuitively first, to the point that you find many exercises in a text book straight forward. Watching 3blue1brown is a good start, but do move forward with deeper treatment. The book I find very usual is David Lay's Linear Algebra and Its Applications: https://www.amazon.com/Linear-Algebra-Its-Applications-5th/d.... Lay sets up a really intuitive geometric framework to explain the intuition of linear transformation with sufficient rigor.

Re: An Intuitive Guide to Linear Algebra (2012)

#46

I... I still really struggle with this. I'm a smart person, I've got a bachelors of engineering, I've been a professional software developer for around 14 years now, and I've built a house. But there is something about degree-level maths and beyond that I find deeply unintuitive in a way that software development isn't. Through comments here I found 3blue1brown's (clearly much loved) videos. By the third video I was…

I used to think this, my problem was that I wasn’t doing the exercises, instead just reading articles and watching videos and trying to get some kind of theoretical understanding. Everything makes a lot more sense once you’ve slogged through a bunch of repeated exercises.

Re: An Intuitive Guide to Linear Algebra (2012)

#47
post #35
post #27

Earlier quoted context omitted.

Once you understand monads, you lose the ability to explain monads. Hence the number of monads tutorials grows at an exponential rate as every new understander tries to explain them and fails. it's a fun problem in teaching

> Once you understand... you lose the ability to explain Sorry, this does not make sense to me.

Douglas Crockford on Monads:

In addition to its being good and useful, it’s also cursed and the curse of the monad is that once you get the epiphany, once you understand - "oh that's what it is" - you lose the ability to explain it to anybody else.

https://youtu.be/dkZFtimgAcM

Re: An Intuitive Guide to Linear Algebra (2012)

#48
post #12

This is ok but nothing is as intuitive as 3B1B's series on YouTube that has been posted hundreds of times on HN [0]. Linear algebra is really about linear transformations of vector spaces, which is not captured in this blog post. [0] https://www.youtube.com/watch?v=fNk_zzaMoSs

Then you failed to comprehend the subject. The point is that a wide array of problems and models are really the same thing.

Re: An Intuitive Guide to Linear Algebra (2012)

#49

I... I still really struggle with this. I'm a smart person, I've got a bachelors of engineering, I've been a professional software developer for around 14 years now, and I've built a house. But there is something about degree-level maths and beyond that I find deeply unintuitive in a way that software development isn't. Through comments here I found 3blue1brown's (clearly much loved) videos. By the third video I was…

Part of the challenge with linear algebra is that a lot of the basics are somewhat dry, since they serve mostly as a way to organize computation -- e.g., a system of linear equations can be expressed as Ax Much of what makes linear algebra interesting and powerful comes from more advanced topics, especially eigenvalues. This power comes when we are not looking at a single matrix in isolation, but when we repeatedly apply a matrix. For instance, consider the equation x_t = A^t x_0. It turns out we can rewrite this an equation by diagonalizing A -- i.e., A = P^{-1} Sigma P, where Sigma is diagonal; most, but not all, matrices can be written in this form. We call s_i the "eigenvalues" of A.

Then, the equation simplifies to x_t = P^{-1} Sigma^t P x_0, or equivalently (P x_t) = Sigma^t (P x_0). This equation is dramatically simpler, since Sigma is diagonal, so if Sigma = diag(s_1, ..., s_n), then Sigma^t = diag(s_1^t, ..., s_n^t). In other words, this transformation "disentangles" the different components of A into ones that act independently. Here, the transformation x -> P x is what is called a "change of basis".

These repeated matrix applications are common in physics, where they represent how a dynamical system evolves over time. The main difference is that in physics, the system evolves continuously, but similar transformations can be applied to solve these problems.

Re: An Intuitive Guide to Linear Algebra (2012)

#50

I... I still really struggle with this. I'm a smart person, I've got a bachelors of engineering, I've been a professional software developer for around 14 years now, and I've built a house. But there is something about degree-level maths and beyond that I find deeply unintuitive in a way that software development isn't. Through comments here I found 3blue1brown's (clearly much loved) videos. By the third video I was…

Higher math involves a very different way of thinking from the typical, useful things people do for a living. Exactness is important. The abstractions can run very deep. It's easy to get lost in the pure side of things without really understanding how to apply it.
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