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Linear Algebra by Jim Hefferon – free textbook

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Re: Linear Algebra by Jim Hefferon – free textbook

#11

What is nice about this book is it includes solutions to exercises. I wish more proof-theoretic books included exercises in the back of the book like this one does. Yes, you can prove something in multiple ways, and no that isn't a good excuse to not include at least one version of the proof in the back of the book. It really benefits the self-learner. The math community seems to have a lot of artificial gatekeeping…

In my experience (math teacher at a community college for 20 years and former Ph.D. student who quit before finishing the thesis) the overwhelming majority of people can not learn mathematics properly from a textbook. They need a teacher or someone to help with problems. It's very difficult to get to a point of really understanding the definition/motivation behind concepts. Even with a teacher it's hard to understand.

Here's a simple example. The distributive property says:

a (b + c) = ab + ac

I can teach students to expand 3(x + 2). With some practice almost all of them will get this. They'll say

3(x+2) = 3x + 3(2) = 3x + 6

Do you know how hard it is to convince people that due to the nature of equality you can reverse the steps? Some never understand that

3x + 6 = 3(x + 2)

Some will never understand that 3x + 2x = 5x because of the distributive property and that combining like terms for the expression 3x + ax is the same process.

I don't think there is any desire to be elitist in terms of having good books that are appropriate. It's just hard to do. We've gone through various cycles of reforming calculus, introducing old concepts in a new way. Through all of the changes one thing has remained constant in my experience. The percentage of people who can get it remains the same.

I do agree with your point on providing solutions.

Re: Linear Algebra by Jim Hefferon – free textbook

#12
post #7

Earlier quoted context omitted.

What are your particular critiques about this book? There's nothing inherently inferior about a free resource. What makes LADR superior to this book? Finding a teacher isn't at all mandatory, you can do math yourself by completing exercises, checking your work, and looking at the solution afterwards. There are plenty of places to ask questions if you get stuck.

> What makes LADR superior to this book? Axler's approach for determinants.

The determinant story of "distortion of unit volume" only makes sense AFAICT if you're in R^n. What does the determinant mean when you're considering linear functions from 2^n to 3^n? There's no geometric interpretation I'm aware of for this case; indeed, I doubt there is one, due to the inherent nature of finite fields.

Re: Linear Algebra by Jim Hefferon – free textbook

#13
post #7

Earlier quoted context omitted.

What are your particular critiques about this book? There's nothing inherently inferior about a free resource. What makes LADR superior to this book? Finding a teacher isn't at all mandatory, you can do math yourself by completing exercises, checking your work, and looking at the solution afterwards. There are plenty of places to ask questions if you get stuck.

> What makes LADR superior to this book? Axler's approach for determinants.

People who are going to be users of applied linear algebra would probably benefit from a traditional treatment of determinants. Axler's book is excellent for people who plan to go for more pure mathematics in their studies.

Re: Linear Algebra by Jim Hefferon – free textbook

#14
If you want to learn linear algebra by coding in python, this is hands down the best book out there.

Coding the Matrix - Philip Klein [0]

It used to have a Coursera course, but I think it's been taken down. The website has videos of the course taught at Brown I think.

The associated website is: http://codingthematrix.com

[0] https://www.amazon.com/Coding-Matrix-Algebra-Applications-Co...

Re: Linear Algebra by Jim Hefferon – free textbook

#15

What is nice about this book is it includes solutions to exercises. I wish more proof-theoretic books included exercises in the back of the book like this one does. Yes, you can prove something in multiple ways, and no that isn't a good excuse to not include at least one version of the proof in the back of the book. It really benefits the self-learner. The math community seems to have a lot of artificial gatekeeping…

Completely in agreement. I really dislike when math books don't have solutions to exercises available, since I self-study.

Like Diestel's Graph Theory is great, it's the book you want to read if you're serious about the subject (D.B. West's book has exercises with solutions, I suppose), but there's absolutely no solutions to be found anywhere; the hints to solutions are now relegated to the "Professional Edition" as well, you can only find hints to old editions online. Makes me question whether or not I understand the material fully, since I can't check work.

Re: Linear Algebra by Jim Hefferon – free textbook

#17
post #11

What is nice about this book is it includes solutions to exercises. I wish more proof-theoretic books included exercises in the back of the book like this one does. Yes, you can prove something in multiple ways, and no that isn't a good excuse to not include at least one version of the proof in the back of the book. It really benefits the self-learner. The math community seems to have a lot of artificial gatekeeping…

In my experience (math teacher at a community college for 20 years and former Ph.D. student who quit before finishing the thesis) the overwhelming majority of people can not learn mathematics properly from a textbook. They need a teacher or someone to help with problems. It's very difficult to get to a point of really understanding the definition/motivation behind concepts. Even with a teacher it's hard to understand…

You make good points.

A person that doesn't understand the distributive property, going into Calculus 1 is not the person that is going to understand Rudin or Spivak on their own without guidance. Yet, people in mathematics communities would recommend Spivak or Rudin anyway and look down on them if they used Stewart or Thomas.

To them if you aren't learning a subject in the fullest rigor possible, then it isn't worth learning. It doesn't matter if the person doesn't even know the basics, they blindly recommend these type of books regardless.

These are excellent books once you already seen the material before, not so much for the average person that doesn't know what the distributive property is.

Re: Linear Algebra by Jim Hefferon – free textbook

#18
post #3

It's nice to have a free book as a supplement. Linear Algebra Done Right by Sheldon Axler is a much better choice and when making an investment in learning, particularly a difficult subject like linear algebra, saving money with a free text is probably the most expensive thing you can do. You might save $40 but end up not really learning and wasting hours you don't have. Above all, find a good teacher.

Axler's Linear Algebra Done Right has always been my favorite linear algebra text (I say this 10+ years after reading it and finishing my math PhD, if that matters).

For those who want a free alternative, behold: Treil's Linear Algebra Done Wrong[2]

The books is downloadable as a free PDF. The name is an answer to Axler's book (dry mathematician's humor), and offers an opposite approach (getting to determinants first).

While I agree with Axler and diagree with Treil, LADW offers way more examples and applications, and together LADR and LADW offer a complete, excellent course material.

---------------------------------------------------------

As for the linked text: not a bad text, but I wouldn't pick it over LADR + LADW.

Here's why:

1. size: it's larger than LADR+LADW taken together. It's hard to see the forest behind the trees.

2. exposition: it follows the structure of many other texts that I don't like because they terribly confuse the students (that I'd have to re-teach afterwards): starting with solving systems of linear equations, then jumping into vector spaces, for example.

3. I don't like how key concepts (matrix product, determinant are introduced). If you already know the material, it will be hard to see what's wrong with the approach of throwing a definition at the reader, and then talking about why that definition was made. But the opposite should be the case.

After teaching Linear Algebra, here's my litmus test for a good book. At a glance, it should make the following clear first and foremost:

1. A matrix of a linear map F is simply writing down the image of the standard basis F(e_1), F(e_2), ... F(e_n). These vectors are the columns of the matrix. If you know them, you can compute F(v) for any v by linearity. That's called "multiplying a vector by matrix"; we write Mv = F(v).

2. The product of matrices is simply the matrix of composition of linear maps that they represent. The student can figure out what that matrix should be (or should be able to do so); here's how. If M is the matrix of F, and N is the matrix of G (where F and G are linear maps), then the first column of MN is F(G(e_1)) = M x (first column of N). Same for other columns. Ta-dah.

3. The determinant of v_1, .. v_n is simply the volume of the lopsided box formed by these vectors (mathematicians call the box "parallelepiped"). In particular, in a plane, the area of the triangle formed by vectors A and B is half the determinant. This are can have a minus sign; switching any pair of vectors flips the sign.

4. Eigenvectors and eigenvalues are fancy words that allow us to describe linear maps like this: "Stretch this picture along these directions by this much". Directions are eigenvectors, by how much - eigenvalues.

Bonus:

5. Rotation and scaling are linear maps. That's all any linear map does: rotates and stretches. Writing a map down in this way is called singular value decomposition.

6. Shears are linear maps that don't change the volume. Any box can be made rectangular by applying a bunch of shears to it. That's called Gaussian elimination or row reduction when you look at what happens to matrices (and apply scaling as the last step). This is also an explanation of why the determinant gives volume (if you define it as an alternating n-linear form).

That's the beginning of a solid understanding of the subject.

From my experience, LADR+LADW leave the student with an understanding of 1-4, and other texts, due to being organized badly, don't (even when they contain all the information in some order).

---------------------------------------------------------

Books I recommend:

[1]LADR: http://linear.axler.net/

[2]LADW: https://www.math.brown.edu/~treil/papers/LADW/LADW.html

Re: Linear Algebra by Jim Hefferon – free textbook

#19
post #18
post #3

It's nice to have a free book as a supplement. Linear Algebra Done Right by Sheldon Axler is a much better choice and when making an investment in learning, particularly a difficult subject like linear algebra, saving money with a free text is probably the most expensive thing you can do. You might save $40 but end up not really learning and wasting hours you don't have. Above all, find a good teacher.

Axler's Linear Algebra Done Right has always been my favorite linear algebra text (I say this 10+ years after reading it and finishing my math PhD, if that matters). For those who want a free alternative, behold: Treil's Linear Algebra Done Wrong[2] The books is downloadable as a free PDF. The name is an answer to Axler's book (dry mathematician's humor), and offers an opposite approach (getting to determinants first…

Grabbing both, thanks!

Re: Linear Algebra by Jim Hefferon – free textbook

#20
post #14

If you want to learn linear algebra by coding in python, this is hands down the best book out there. Coding the Matrix - Philip Klein [0] It used to have a Coursera course, but I think it's been taken down. The website has videos of the course taught at Brown I think. The associated website is: http://codingthematrix.com [0] https://www.amazon.com/Coding-Matrix-Algebra-Applications-Co...

The course is available here: http://academictorrents.com/details/54cd86f3038dfd446b037891...

It is legal, not a pirated version.

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