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Differential Forms and Integration (2008) [pdf]

math.ucla.edu

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Re: Differential Forms and Integration (2008) [pdf]

#41

I took a Differential Geometry course in university. The course covered basic theory on smooth manifolds and Riemannian Geometry. While I did appreciate the beauty of the subject from a theoretical perspective, I have to admit that I somewhat lacked intuition for the material, especially with regards to differential forms. I understood that their properties make sense to define the notion of integration on a smooth m…

The point of differential forms is that they give a way to express geometric theorems in a coordinate free way. Coordinates are seen as obscuring the pure geometric content of theorems. They are sometimes necessary artifacts of doing concrete calculations, but the idea is that geometry shouldn't depend on a choice of coordinates. The important ideas can be found in pages 9-10 in this link: https://www.math.ucla.edu/~…

> [...] but the idea is that geometry shouldn't depend on a choice of coordinates

Indeed, in "Tensor Geometry" (Dodson & Poston), they note:

> Most modern "differential geometry" texts use a coordinate-free notation almost throughout. This is excellent for a coherent understanding, but leaves the physics student quite unequipped for the physical literature, or for the specific physical computations in which coordinates are unavoidable. Even when the relation to classical notation is explained, as in the magnificent [Spivak], pseudo-Riemannian geometry is barely touched on. This is crippling to the physicist, for whom spacetime is the most important example, and perverse even for the geometer. Indefinite metrics arise as easily within pure mathematics (for instance in Lie group theory) as in applications, and the mathematician should know the differences between such geometries and the positive definite type. In this book therefore we treat both cases equally, and describe both relativity theory and (in Ch. IX, §6) an important "abstract" pseudo Riemannian space, SL(2;R).

Re: Differential Forms and Integration (2008) [pdf]

#42
post #36
post #10

Earlier quoted context omitted.

I love Hubbard & Hubbard, which is also great as it's an introductory text. It's been used often at Harvard Math 55 and some much simpler courses: http://matrixeditions.com/#vec

That is indeed a very good book. Although I would say that some of the notation in it is non-standard, for better or for worse. Tu is the most consistent author I have ever seen with notation, and that matters a lot in smooth manifold theory and differential geometry. Another good book is Advanced Calculus: A Geometric View by James Callahan.

> Another good book is Advanced Calculus: A Geometric View by James Callahan.

Thank you for this! For those of us who had real difficulty with Advanced Calculus, Callahan's methodical, visual, generous approach is deeply felt and appreciated. I did not know of this book until now and immediately found myself absorbed. It's embarrassing to admit, but as one who loves mathematics yet seems to struggle and stagnate more often than everyone around me, I often want to ask for, and indeed need, a bit of hand-holding. Callahan is a wonderful guide in that sense. Thanks again.

Re: Differential Forms and Integration (2008) [pdf]

#43
post #42
post #36

Earlier quoted context omitted.

That is indeed a very good book. Although I would say that some of the notation in it is non-standard, for better or for worse. Tu is the most consistent author I have ever seen with notation, and that matters a lot in smooth manifold theory and differential geometry. Another good book is Advanced Calculus: A Geometric View by James Callahan.

> Another good book is Advanced Calculus: A Geometric View by James Callahan. Thank you for this! For those of us who had real difficulty with Advanced Calculus, Callahan's methodical, visual, generous approach is deeply felt and appreciated. I did not know of this book until now and immediately found myself absorbed. It's embarrassing to admit, but as one who loves mathematics yet seems to struggle and stagnate more…

No problem. It is a great book.

Definitely check out Edwards' book I mentioned above as well. It is a gem of a book. Although it doesn't use matrices and instead uses linear expansions, it is still brilliant. The first three chapters give an exposition of the theory, and then the next three go back and prove things. So if anything, take a look at the first three chapters and then the later ones on applications and extensions. It also has a geometrical viewpoint.

Re: Differential Forms and Integration (2008) [pdf]

#44
post #3

Can anyone recommend a good introduction to differential geometry and forms? Does something analogous to "Visual Complex Analysis" exist for the topic? I have been curious to learn for a long time but, for whatever reason, always lose my way at some point with articles like this. I come away with some feeling that I understand what's going on and yet I can't say I have any concrete intuition for what a form or a mani…

I listed references elsewhere.

https://news.ycombinator.com/item?id=23270163

Edwards' first three chapters give a wonderfullly intuitive exposition of forms and their application to integration.

Tu's book is a rigourous study of smooth manifolds and differential forms. His exercises are approachable, and his book is the most expedient to the full theory of differential forms.

As a quirky intuition pump, I recommend Geometrical Vectors by Gabriel Weinreich. The Fortney book mentioned in another comment is a nice, visual book, and there are other references in the replies to the comment I linked.

Re: Differential Forms and Integration (2008) [pdf]

#45
post #4
post #3

Can anyone recommend a good introduction to differential geometry and forms? Does something analogous to "Visual Complex Analysis" exist for the topic? I have been curious to learn for a long time but, for whatever reason, always lose my way at some point with articles like this. I come away with some feeling that I understand what's going on and yet I can't say I have any concrete intuition for what a form or a mani…

A Visual Introduction to Differential Forms and Calculus on Manifolds by Jon Fortney. https://www.amazon.com/Visual-Introduction-Differential-Calc...

I got this recently from Springer directly, and just as a psudeo-warning, this is a "print on demand" book, at least the one I got was (it said so when I ordered it, so I was properly warned). Now, the print is actually pretty high quality and so is the binding, and it's a large and beautiful book. My only complaint is the paper of the pages is a bit thin, like regular printer paper stock, as opposed to the thicker glossy paper I was hoping for and that would be usual for a book this size. When you're leafing through it and a page is lifted, you can often see the content on the opposite side showing through. That can be distracting and may bother some people.

BTW: If you buy from Springer, you get a free pdf of the book immediately while you wait for your physical copy, because of the delay for print on demand. They say you don't actually "own" the digital edition (can't remember the exact wording), but I can vouch that it's not time-limited. It's a very good deal.

Re: Differential Forms and Integration (2008) [pdf]

#46

I don't think the distinction between the signed and unsigned integral exists for the most general integral, the Henstock-Kurzweil integral. (I could be wrong, but an orientation seems to always be implied in being able to compute a Riemann sum over a tagged partition.) This distinction is probably related to the Lebesgue integral's inability to integrate functions unless they are absolutely integrable (since it need…

Wikipedia says there's an even more general integral ( https://en.wikipedia.org/wiki/Khinchin_integral )? https://en.wikipedia.org/wiki/Henstock%E2%80%93Kurzweil_inte...

General in the sense that it integrates more functions. The Denjoy integral is equivalent to the Henstock-Kurzweil integral in that respect (Theories of Integration - The integrals of Riemann, Lebesgue, Henstock-Kurzweil, and McShane, Kurtz & Swartz).

Re: Differential Forms and Integration (2008) [pdf]

#47
post #17

I don't think the distinction between the signed and unsigned integral exists for the most general integral, the Henstock-Kurzweil integral. (I could be wrong, but an orientation seems to always be implied in being able to compute a Riemann sum over a tagged partition.) This distinction is probably related to the Lebesgue integral's inability to integrate functions unless they are absolutely integrable (since it need…

I'm not sure gauge integrals are really "the most general integral". As you say, it doesn't work as well as the Lebesgue integral in multidimensional settings, does it? It also needs a bit of a tweak to give you the analogue of Stieltjes integration so you can unify sums and integrals, I believe.

They are the most general in the sense that there are Henstock-Kurzweil integrable functions that are not Lebesgue integrable and that other integrals that are also more general than the Lebesgue integrals are equivalent to the Henstock-Kurzweil integral.

It still works better than the Lebesgue integral in the multidimensional settings, since it is trivial to create a product f(x)g(y) of two functions which will not be Lebesgue integrable but is Henstock-Kurzweil integrable.

As for generalizations to generalized functions, my preference lies with Colombeau algebras over Schwartz distributions, in any case. Where at least there is an arithmetic of the generalized functions.

Re: Differential Forms and Integration (2008) [pdf]

#48
post #45
post #4

Earlier quoted context omitted.

A Visual Introduction to Differential Forms and Calculus on Manifolds by Jon Fortney. https://www.amazon.com/Visual-Introduction-Differential-Calc...

I got this recently from Springer directly, and just as a psudeo-warning, this is a "print on demand" book, at least the one I got was (it said so when I ordered it, so I was properly warned). Now, the print is actually pretty high quality and so is the binding, and it's a large and beautiful book. My only complaint is the paper of the pages is a bit thin, like regular printer paper stock, as opposed to the thicker g…

Having gone through two chapters now, I also feel the need to caution others that the amount of typos in this book is simply jaw-dropping. The conceptual explanations in the text are generally excellent, but it is simply impossible to get through a page without hitting a substantial number of mistakes. I'm left wondering if there are errors I'm not catching on my own that are going to affect my understanding. I really hope a cleaned up second edition is on the horizon (hopefully with answers to some of the in-line exercises).
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