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Disclaimer: I have studied linear algebra with your book. Thank you for writing it. Special thanks for making it completely free and open-source.

I have gotten a fair number of emails along the lines of "I'd like to adopt your book but since anyone can download the answers, I cannot teach out of it."

When we had an introductory course in linear algebra, we were not given any home assignments. Instead, we were told that if we want to train and exercise some concepts, we should find third-party materials and self-study -- and so, I used your book. I really like that approach, it allows more capable students to do whatever they like instead, and to less capable -- work on it, if needed. Thus, I don't understand the rationale of not teaching out of something that contains solved exercises, because there is no reason to assign mandatory exercises in the first place. It's enough to have tests.

And of course, such books are extremely valuable for non-mainstream (that is, not enrolled into a high school or wherever) audience, which can be smaller, but has more impact regarding feedback.

Not all resources are of similar quality and profs aren't going to let the students judge that for themselves. I imagine a prof wants questions that specifically walk students through what they are teaching.

>I have been told that it is work only appropriate for grad students.

It's quite common to look down on "lesser" work like this (janitorial work, writing solutions, whaterver) as only useful for those "lower" than you, but the amount of times I asked for help from a professor only to have them struggle to comprehend how to solve the problem (from their own assignment) was too damn high. Maybe if they tried to eat their own dog food, they'd see where they could improve.

>They ask about adoptions.

Of course, because the metrics we used to use to get a gauge of where we were progressing and where we needed work turned directly into a measure of our worth as a laborer. Your worth as a professor is only proportional to how much good PR you bring to your organization, they don't care about you actually teaching students, especially not students who aren't paying for your services via your university tuition.

Thank you for writing this book and providing it as a free resource for the audience that I have in mind. I downloaded your book and plan to work through it in its entirety. Coincidentally I am studying linear algebra, so this is a perfect resource for me. The coverage of your material looks very good, so I am excited to work through it.

I have admit it's one of the nicest math books laid out in LaTeX, it's a pleasure read.

That's kind of you; thank you.

Thank you very much for creating your books and making them freely available. You are truly "doing God's work" (so to speak).

Though I have only skimmed through the textbook, it looks very well written. I admire the effort you have put into it, and that you have made it available for free. The same thing holds for the text on number theory (although it looks like you have put even more effort in the linear algebra text - not only due to the fancy typesetting).

How much time did you put into writing? I have been wishing to write something similar (that is, math texts about linear algebra, analysis, number theory, etc.) for a long time, although I can only hope it to be of this quality. Do you have any tips for an aspiring math textbook writer? I have a graduate degree in math, but I unfortunately I don't use math in my day job, so I am afraid that the material I produce will be too low in quality to be useful for people...

I'm sorry but I missed your question earlier. I am currently working on a Theory of Computation text. I have about two years in, and anticipate at least one more, probably two. (I need to write some Scheme and I am rusty.)

No worries, I just posted this yesterday! ;) I know how busy professors can be, so I wasn't really expecting a reply (at least anytime soon).

But wow, that is a pretty deep investment! I was expecting a little less, but I guess it makes sense since writing is not your full-time occupation.

I work at a small liberal arts college, St Michael's College in Vermont. I have a much greater expectation of teaching effort than professors at research institutions would have, although here there is also an expectation of professional activity. So the writing is not anything like full-time. But it is a creative outlet, which is great.

> I have a graduate degree in math, but I unfortunately I don't use math in my day job, so I am afraid that the material I produce will be too low in quality to be useful for people...

It is good to have feedback from real people. I work through material with my students in classes, and sometimes I've had what I thought was a great approach and it would just not work in practice.

I don't know if there are online groups of people working on writng stuff like this, either at the college level or at high school or earlier levels, but if you could find such a group, it'd be good to get in with them. (And tell me. :-) )

Have you considered taking up the textbook model of providing answers to only a subset of the questions?

When I first provided the book (?96), with it I provided for free download the answers to about half of the questions. The web page said something like, "If you are an instructor then write me and I'll give you access to the rest." But just how foolish that was quickly became apparent: telling who is acutally an instructor or someone learning on their own, and not someone just saying that, was not something that I could do.

Publishers reps seem to me to rely on paper mail, and an address like "Math Dept, St Michael's College" does provide some kind of proof. But I sometimes get emails like "I am a student in a poor country and the only way ..." and I simply am not saying no to that.

That last sentence also answers why I don't erase half of the answers.

Free texts are a different model and there are a lot of kinks.

The folks who wrote the book this thread is based on have done something great. (I teach Discrete and I had a look to see if I could use it.) But including answers is a problem to which I am unaware of a solution. Or maybe, it is just that expectations have to change.

Maybe your problem is just being overly consistent? Wouldn't just making half the answers officially available, but not troubling yourself overly over whether you can validate that someone really is an instructor allow you to you to have your cake and eat it too? As you point out, the profs who think they can't teach out of a book with officially available answers are probably deluded anyway, and the answers not being "officially" available might be enough to satisfy them (and thus for you to reap the academic reward for your effort you deserve). A text book with available answers is a so much greater public good, it's disheartening to see you penalized for it.

The obvious solution would be to not provide access to the even-numbered answers to anyone. Students in poor countries would presumably be able to study with just the odd numbered questions (after all, university students are expected to do so). Requests from instructors could be answered with "If you can't solve these problems yourself, you have no business assigning them as homework.", or, if you're feeling particularly Kafkaesque, assume the're all actually students and congratulate them on having a particularly convincing return address, but no, you're still not going to help them cheat.

This does call for a rather more misanthropic attitude than you seem to have, though.

Last summer, around the time my mom passed, someone who teaches out of my book sent me a picture of her class. Just by coincidence this was near to where my mom and dad grew up in the 1940's. It was a room of bright people, all kinds of shades, who wanted the American dream and were working through Linear Algebra on their way up there.

So no, I'm not doing that. :-)

Please continue to stay steadfast in your approach in teaching mathematics and providing solutions. I bought your book, and love the fact you provide it freely online for all to use. Your approach addressed all of the concerns I had in my initial post and I see your book maintains mathematical rigor. This is honestly a breathe of fresh air. Thank you again. You are truly serving the ones that want to learn.

As the other commenter mentioned, it's beautifully typeset, do you have any hints for someone who writes a fair bit of math in LaTeX?

I think of it as very generic LaTeX. I use the AMS math styles for formatting the equations. The fonts are not the standard ones, but they were chosen for xerox-ability rather than some aesthetic (which I don't have). Other than that it is straightforward. (The LaTeX is at https://gitlab.com/jim.hefferon/linear-algebra .)

AMS Euler should be much more widely used. It’s great.

https://en.wikipedia.org/wiki/AMS_Euler

Algorithm books are the same way. No solutions. They ought to have a question section for professors to test and a separate question section for students to practice. It doesn't have to be one size fits all.